diff --git a/async/chain.ts b/async/chain.ts
new file mode 100644
index 0000000..cb1a99f
--- /dev/null
+++ b/async/chain.ts
@@ -0,0 +1,24 @@
+/**
+ * Chains multiple iterables together.
+ *
+ * @param iterables The iterables to chain.
+ * @returns The chained iterable.
+ * @example
+ *
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { chain } from "@core/iterutil/async/chain";
+ *
+ * const iter = chain([1, 2], [3, 4]);
+ * console.log(await toArray(iter)); // [1, 2, 3, 4]
+ * ```
+ */
+export async function* chain<T>(
+  ...iterables: Iterable<T>[] | AsyncIterable<T>[]
+): AsyncIterable<T> {
+  for await (const iterable of iterables) {
+    for await (const value of iterable) {
+      yield value;
+    }
+  }
+}
diff --git a/async/chain_test.ts b/async/chain_test.ts
new file mode 100644
index 0000000..df7393b
--- /dev/null
+++ b/async/chain_test.ts
@@ -0,0 +1,25 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { chain } from "./chain.ts";
+
+Deno.test("chain", async (t) => {
+  await t.step("with async iterable", async () => {
+    const result = chain(
+      toAsyncIterable([1, 2]),
+      toAsyncIterable([3, 4]),
+      toAsyncIterable([5]),
+    );
+    const expected = [1, 2, 3, 4, 5];
+    assertEquals(await toArray(result), expected);
+    assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+  });
+
+  await t.step("with iterable", async () => {
+    const result = chain([1, 2], [3, 4], [5]);
+    const expected = [1, 2, 3, 4, 5];
+    assertEquals(await toArray(result), expected);
+    assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+  });
+});
diff --git a/async/chunked.ts b/async/chunked.ts
new file mode 100644
index 0000000..e9cd288
--- /dev/null
+++ b/async/chunked.ts
@@ -0,0 +1,32 @@
+/**
+ * Chunks an iterable into arrays of a given size.
+ *
+ * @param iterable The iterable to chunk.
+ * @param size The size of each chunk.
+ * @returns The chunked iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { chunked } from "@core/iterutil/async/chunked";
+ *
+ * const iter = chunked([1, 2, 3, 4, 5], 2);
+ * console.log(await toArray(iter)); // [[1, 2], [3, 4], [5]]
+ * ```
+ */
+export async function* chunked<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  size: number,
+): AsyncIterable<T[]> {
+  let chunk = [];
+  for await (const item of iterable) {
+    chunk.push(item);
+    if (chunk.length === size) {
+      yield chunk;
+      chunk = [];
+    }
+  }
+  if (chunk.length > 0) {
+    yield chunk;
+  }
+}
diff --git a/async/chunked_test.ts b/async/chunked_test.ts
new file mode 100644
index 0000000..9b38a15
--- /dev/null
+++ b/async/chunked_test.ts
@@ -0,0 +1,67 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { chunked } from "./chunked.ts";
+
+Deno.test("chunked", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("the length is divisible by the size", async () => {
+      const result = chunked(toAsyncIterable([1, 2, 3, 4, 5, 6]), 2);
+      const expected = [[1, 2], [3, 4], [5, 6]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+
+    await t.step("the length is not divisible by the size", async () => {
+      const result = chunked(toAsyncIterable([1, 2, 3, 4, 5]), 2);
+      const expected = [[1, 2], [3, 4], [5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+
+    await t.step("the length is equal to the size", async () => {
+      const result = chunked(toAsyncIterable([1, 2, 3, 4, 5]), 5);
+      const expected = [[1, 2, 3, 4, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+
+    await t.step("the length is less than the size", async () => {
+      const result = chunked(toAsyncIterable([1, 2, 3, 4, 5]), 6);
+      const expected = [[1, 2, 3, 4, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("the length is divisible by the size", async () => {
+      const result = chunked([1, 2, 3, 4, 5, 6], 2);
+      const expected = [[1, 2], [3, 4], [5, 6]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+
+    await t.step("the length is not divisible by the size", async () => {
+      const result = chunked([1, 2, 3, 4, 5], 2);
+      const expected = [[1, 2], [3, 4], [5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+
+    await t.step("the length is equal to the size", async () => {
+      const result = chunked([1, 2, 3, 4, 5], 5);
+      const expected = [[1, 2, 3, 4, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+
+    await t.step("the length is less than the size", async () => {
+      const result = chunked([1, 2, 3, 4, 5], 6);
+      const expected = [[1, 2, 3, 4, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+  });
+});
diff --git a/async/compact.ts b/async/compact.ts
new file mode 100644
index 0000000..92ec059
--- /dev/null
+++ b/async/compact.ts
@@ -0,0 +1,24 @@
+/**
+ * Removes all nullish values from an iterable.
+ *
+ * @param iterable The iterable to compact.
+ * @returns The compacted iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { compact } from "@core/iterutil/async/compact";
+ *
+ * const iter = compact([1, undefined, 2, null, 3]);
+ * console.log(await toArray(iter)); // [1, 2, 3]
+ * ```
+ */
+export async function* compact<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): AsyncIterable<NonNullable<T>> {
+  for await (const value of iterable) {
+    if (value != null) {
+      yield value;
+    }
+  }
+}
diff --git a/async/compact_test.ts b/async/compact_test.ts
new file mode 100644
index 0000000..f0204f0
--- /dev/null
+++ b/async/compact_test.ts
@@ -0,0 +1,91 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { compact } from "./compact.ts";
+
+Deno.test("compact", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("without undefined/null", async () => {
+      const result = compact(toAsyncIterable([1, 2, 3, 4, 5]));
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with undefined", async () => {
+      const result = compact(toAsyncIterable([
+        undefined,
+        1,
+        2,
+        undefined,
+        3,
+        undefined,
+        4,
+        5,
+        undefined,
+      ]));
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with null", async () => {
+      const result = compact(
+        toAsyncIterable([null, 1, 2, null, 3, null, 4, 5, null]),
+      );
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with undefined/null", async () => {
+      const result = compact(
+        toAsyncIterable([undefined, 1, 2, null, 3, undefined, 4, 5, null]),
+      );
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("without undefined/null", async () => {
+      const result = compact([1, 2, 3, 4, 5]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with undefined", async () => {
+      const result = compact([
+        undefined,
+        1,
+        2,
+        undefined,
+        3,
+        undefined,
+        4,
+        5,
+        undefined,
+      ]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with null", async () => {
+      const result = compact([null, 1, 2, null, 3, null, 4, 5, null]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with undefined/null", async () => {
+      const result = compact([undefined, 1, 2, null, 3, undefined, 4, 5, null]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/compress.ts b/async/compress.ts
new file mode 100644
index 0000000..9d75e04
--- /dev/null
+++ b/async/compress.ts
@@ -0,0 +1,39 @@
+/**
+ * Compress an iterable by selecting elements using a selector iterable.
+ *
+ * @param iterable The iterable to compress.
+ * @param selectors The selectors to use.
+ * @returns The compressed iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { compress } from "@core/iterutil/async/compress";
+ *
+ * const iter = compress([1, 2, 3, 4, 5], [true, false, true, false, true]);
+ * console.log(await toArray(iter)); // [1, 3, 5]
+ * ```
+ */
+export async function* compress<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  selectors: Iterable<boolean> | AsyncIterable<boolean>,
+): AsyncIterable<T> {
+  const it1 = Symbol.iterator in iterable
+    ? iterable[Symbol.iterator]()
+    : iterable[Symbol.asyncIterator]();
+  const it2 = Symbol.iterator in selectors
+    ? selectors[Symbol.iterator]()
+    : selectors[Symbol.asyncIterator]();
+  while (true) {
+    const [
+      { done: done1, value: value1 },
+      { done: done2, value: value2 },
+    ] = await Promise.all([it1.next(), it2.next()]);
+    if (done1 || done2) {
+      break;
+    }
+    if (value2) {
+      yield value1;
+    }
+  }
+}
diff --git a/async/compress_test.ts b/async/compress_test.ts
new file mode 100644
index 0000000..b368caa
--- /dev/null
+++ b/async/compress_test.ts
@@ -0,0 +1,68 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { compress } from "./compress.ts";
+
+Deno.test("compress", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("the iterable and the selectors are same length", async () => {
+      const result = compress(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        toAsyncIterable([true, false, true, false, true]),
+      );
+      const expected = [1, 3, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("the iterable is larger than the selectors", async () => {
+      const result = compress(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        toAsyncIterable([true, false, true]),
+      );
+      const expected = [1, 3];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("the iterable is smaller than the selector", async () => {
+      const result = compress(
+        toAsyncIterable([1, 2, 3]),
+        toAsyncIterable([true, false, true, false, true]),
+      );
+      const expected = [1, 3];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("the iterable and the selectors are same length", async () => {
+      const result = compress([1, 2, 3, 4, 5], [
+        true,
+        false,
+        true,
+        false,
+        true,
+      ]);
+      const expected = [1, 3, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("the iterable is larger than the selectors", async () => {
+      const result = compress([1, 2, 3, 4, 5], [true, false, true]);
+      const expected = [1, 3];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("the iterable is smaller than the selector", async () => {
+      const result = compress([1, 2, 3], [true, false, true, false, true]);
+      const expected = [1, 3];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/cycle.ts b/async/cycle.ts
new file mode 100644
index 0000000..66a4867
--- /dev/null
+++ b/async/cycle.ts
@@ -0,0 +1,30 @@
+/**
+ * Returns an infinite iterable that cycles through the given iterable.
+ *
+ * @param iterable The iterable to cycle.
+ * @returns The cycled iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { cycle } from "@core/iterutil/async/cycle";
+ * import { take } from "@core/iterutil/async/take";
+ *
+ * const iter = cycle([1, 2, 3]);
+ * console.log(await toArray(take(iter, 5))); // [1, 2, 3, 1, 2]
+ * ```
+ */
+export async function* cycle<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): AsyncIterable<T> {
+  const array: T[] = [];
+  for await (const item of iterable) {
+    array.push(item);
+  }
+  if (array.length === 0) {
+    return;
+  }
+  while (true) {
+    yield* array;
+  }
+}
diff --git a/async/cycle_test.ts b/async/cycle_test.ts
new file mode 100644
index 0000000..069deab
--- /dev/null
+++ b/async/cycle_test.ts
@@ -0,0 +1,54 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { take } from "./take.ts";
+import { cycle } from "./cycle.ts";
+
+Deno.test("cycle", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = cycle(toAsyncIterable([0, 1, 2]));
+      const expected = [0, 1, 2, 0, 1];
+      assertEquals(await toArray(take(result, 5)), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with single value iterable", async () => {
+      const result = cycle(toAsyncIterable([0]));
+      const expected = [0, 0, 0, 0, 0];
+      assertEquals(await toArray(take(result, 5)), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = cycle(toAsyncIterable([] as number[]));
+      const expected: number[] = [];
+      assertEquals(await toArray(take(result, 5)), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = cycle([0, 1, 2]);
+      const expected = [0, 1, 2, 0, 1];
+      assertEquals(await toArray(take(result, 5)), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with single value iterable", async () => {
+      const result = cycle([0]);
+      const expected = [0, 0, 0, 0, 0];
+      assertEquals(await toArray(take(result, 5)), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = cycle([] as number[]);
+      const expected: number[] = [];
+      assertEquals(await toArray(take(result, 5)), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/drop.ts b/async/drop.ts
new file mode 100644
index 0000000..e979d27
--- /dev/null
+++ b/async/drop.ts
@@ -0,0 +1,36 @@
+/**
+ * Drops the first `limit` items from the iterable.
+ *
+ * It throws an error if `limit` is less than 0.
+ *
+ * @param iterable The iterable to drop items from.
+ * @param limit The number of items to drop.
+ * @returns The iterable with the first `limit` items dropped.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { drop } from "@core/iterutil/async/drop";
+ *
+ * const iter = drop([1, 2, 3, 4, 5], 2);
+ * console.log(await toArray(iter)); // [3, 4, 5]
+ * ```
+ */
+export function drop<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  limit: number,
+): AsyncIterable<T> {
+  if (limit < 0) {
+    throw new Error(
+      `limit argument must be greater than or equal to 0, but got ${limit}.`,
+    );
+  }
+  return async function* () {
+    let i = 0;
+    for await (const item of iterable) {
+      if (i++ >= limit) {
+        yield item;
+      }
+    }
+  }();
+}
diff --git a/async/drop_test.ts b/async/drop_test.ts
new file mode 100644
index 0000000..0223e2d
--- /dev/null
+++ b/async/drop_test.ts
@@ -0,0 +1,59 @@
+import { assertEquals, assertThrows } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { drop } from "./drop.ts";
+
+Deno.test("drop", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with positive limit", async () => {
+      const result = drop(toAsyncIterable([0, 1, 2, 3, 4]), 2);
+      const expected = [2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with negative limit", () => {
+      assertThrows(
+        () => {
+          drop([0, 1, 2, 3, 4], -2);
+        },
+        Error,
+        "limit argument must be greater than or equal to 0, but got -2.",
+      );
+    });
+
+    await t.step("with 0 limit", async () => {
+      const result = drop(toAsyncIterable([0, 1, 2, 3, 4]), 0);
+      const expected = [0, 1, 2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with positive limit", async () => {
+      const result = drop([0, 1, 2, 3, 4], 2);
+      const expected = [2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with negative limit", () => {
+      assertThrows(
+        () => {
+          drop([0, 1, 2, 3, 4], -2);
+        },
+        Error,
+        "limit argument must be greater than or equal to 0, but got -2.",
+      );
+    });
+
+    await t.step("with 0 limit", async () => {
+      const result = drop([0, 1, 2, 3, 4], 0);
+      const expected = [0, 1, 2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/drop_while.ts b/async/drop_while.ts
new file mode 100644
index 0000000..efc04c0
--- /dev/null
+++ b/async/drop_while.ts
@@ -0,0 +1,32 @@
+/**
+ * Drops elements from the iterable while the predicate returns true.
+ *
+ * The first element that does not match the predicate is included in the output.
+ * If the predicate never returns false, the output will be an empty iterable.
+ *
+ * @param iterable The iterable to drop elements from.
+ * @param fn The predicate function to drop elements with.
+ * @returns The iterable with elements dropped while the predicate returns true.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { dropWhile } from "@core/iterutil/async/drop-while";
+ *
+ * const iter = dropWhile([1, 2, 3, 4, 5], (x) => x < 3);
+ * console.log(await toArray(iter)); // [3, 4, 5]
+ * ```
+ */
+export async function* dropWhile<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T) => boolean | Promise<boolean>,
+): AsyncIterable<T> {
+  let dropping = true;
+  for await (const value of iterable) {
+    if (dropping && await fn(value)) {
+      continue;
+    }
+    dropping = false;
+    yield value;
+  }
+}
diff --git a/async/drop_while_test.ts b/async/drop_while_test.ts
new file mode 100644
index 0000000..b16b19a
--- /dev/null
+++ b/async/drop_while_test.ts
@@ -0,0 +1,70 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { dropWhile } from "./drop_while.ts";
+
+Deno.test("dropWhile", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with some true", async () => {
+      const result = dropWhile(toAsyncIterable([0, 1, 2, 3, 4]), (v) => v < 2);
+      const expected = [2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with some promise true", async () => {
+      const result = dropWhile(
+        toAsyncIterable([0, 1, 2, 3, 4]),
+        (v) => Promise.resolve(v < 2),
+      );
+      const expected = [2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all true", async () => {
+      const result = dropWhile(toAsyncIterable([0, 1, 2, 3, 4]), () => true);
+      const expected: number[] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all false", async () => {
+      const result = dropWhile(toAsyncIterable([0, 1, 2, 3, 4]), () => false);
+      const expected = [0, 1, 2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with some true", async () => {
+      const result = dropWhile([0, 1, 2, 3, 4], (v) => v < 2);
+      const expected = [2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with some promise true", async () => {
+      const result = dropWhile([0, 1, 2, 3, 4], (v) => Promise.resolve(v < 2));
+      const expected = [2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all true", async () => {
+      const result = dropWhile([0, 1, 2, 3, 4], () => true);
+      const expected: number[] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all false", async () => {
+      const result = dropWhile([0, 1, 2, 3, 4], () => false);
+      const expected = [0, 1, 2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/enumerate.ts b/async/enumerate.ts
new file mode 100644
index 0000000..c92e9ed
--- /dev/null
+++ b/async/enumerate.ts
@@ -0,0 +1,27 @@
+/**
+ * Enumerate an iterable.
+ *
+ * @param iterable The iterable to enumerate.
+ * @param start The starting index.
+ * @returns An iterable of index-value pairs.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { enumerate } from "@core/iterutil/async/enumerate";
+ *
+ * const iter = enumerate(["a", "b", "c"]);
+ * console.log(await toArray(iter)); // [[0, "a"], [1, "b"], [2, "c"]]
+ * ```
+ */
+export async function* enumerate<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  start: number = 0,
+  step: number = 1,
+): AsyncIterable<[number, T]> {
+  let i = start;
+  for await (const value of iterable) {
+    yield [i, value];
+    i += step;
+  }
+}
diff --git a/async/enumerate_test.ts b/async/enumerate_test.ts
new file mode 100644
index 0000000..dd8428e
--- /dev/null
+++ b/async/enumerate_test.ts
@@ -0,0 +1,53 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { enumerate } from "./enumerate.ts";
+
+Deno.test("enumerate", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("default", async () => {
+      const result = enumerate(toAsyncIterable([0, 1, 2]));
+      const expected = [[0, 0], [1, 1], [2, 2]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with start", async () => {
+      const result = enumerate(toAsyncIterable([0, 1, 2]), 1);
+      const expected = [[1, 0], [2, 1], [3, 2]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with start/step", async () => {
+      const result = enumerate(toAsyncIterable([0, 1, 2]), 1, 2);
+      const expected = [[1, 0], [3, 1], [5, 2]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("default", async () => {
+      const result = enumerate([0, 1, 2]);
+      const expected = [[0, 0], [1, 1], [2, 2]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with start", async () => {
+      const result = enumerate([0, 1, 2], 1);
+      const expected = [[1, 0], [2, 1], [3, 2]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with start/step", async () => {
+      const result = enumerate([0, 1, 2], 1, 2);
+      const expected = [[1, 0], [3, 1], [5, 2]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+  });
+});
diff --git a/async/every.ts b/async/every.ts
new file mode 100644
index 0000000..7ffdd86
--- /dev/null
+++ b/async/every.ts
@@ -0,0 +1,27 @@
+/**
+ * Returns true if every element in the iterable satisfies the provided testing function.
+ *
+ * @param iterable The iterable to test.
+ * @param fn The function to test with.
+ * @returns True if every element in the iterable satisfies the provided testing function, otherwise false.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { every } from "@core/iterutil/async/every";
+ *
+ * console.log(await every([1, 2, 3], (value) => value > 0)); // true
+ * console.log(await every([1, 2, 3], (value) => value > 1)); // false
+ * ```
+ */
+export async function every<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T) => boolean | Promise<boolean>,
+): Promise<boolean> {
+  for await (const value of iterable) {
+    if (!await fn(value)) {
+      return false;
+    }
+  }
+  return true;
+}
diff --git a/async/every_test.ts b/async/every_test.ts
new file mode 100644
index 0000000..5fe0b32
--- /dev/null
+++ b/async/every_test.ts
@@ -0,0 +1,84 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { every } from "./every.ts";
+
+Deno.test("every", async (t) => {
+  await t.step("with iterable", async (t) => {
+    await t.step("true", async () => {
+      const result = await every(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (v) => v > 0,
+      );
+      const expected = true;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("false", async () => {
+      const result = await every(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (v) => v > 1,
+      );
+      const expected = false;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("promise true", async () => {
+      const result = await every(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (v) => Promise.resolve(v > 0),
+      );
+      const expected = true;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("promise false", async () => {
+      const result = await every(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (v) => Promise.resolve(v > 1),
+      );
+      const expected = false;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("true", async () => {
+      const result = await every([1, 2, 3, 4, 5], (v) => v > 0);
+      const expected = true;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("false", async () => {
+      const result = await every([1, 2, 3, 4, 5], (v) => v > 1);
+      const expected = false;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("promise true", async () => {
+      const result = await every(
+        [1, 2, 3, 4, 5],
+        (v) => Promise.resolve(v > 0),
+      );
+      const expected = true;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("promise false", async () => {
+      const result = await every(
+        [1, 2, 3, 4, 5],
+        (v) => Promise.resolve(v > 1),
+      );
+      const expected = false;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+  });
+});
diff --git a/async/filter.ts b/async/filter.ts
new file mode 100644
index 0000000..9ad9b58
--- /dev/null
+++ b/async/filter.ts
@@ -0,0 +1,27 @@
+/**
+ * Filters an iterable based on a function.
+ *
+ * @params iterable The iterable to filter.
+ * @params fn The function to filter with.
+ * @returns The filtered iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { filter } from "@core/iterutil/async/filter";
+ *
+ * const iter = filter([1, 2, 3, 4, 5], (value) => value % 2 === 0);
+ * console.log(await toArray(iter)); // [2, 4]
+ * ```
+ */
+export async function* filter<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T, index: number) => boolean | Promise<boolean>,
+): AsyncIterable<T> {
+  let index = 0;
+  for await (const value of iterable) {
+    if (await fn(value, index++)) {
+      yield value;
+    }
+  }
+}
diff --git a/async/filter_test.ts b/async/filter_test.ts
new file mode 100644
index 0000000..647cab7
--- /dev/null
+++ b/async/filter_test.ts
@@ -0,0 +1,77 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { filter } from "./filter.ts";
+
+Deno.test("filter", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("without promise", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = filter(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return value % 2 === 0;
+        },
+      );
+      const expected = [2, 4];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with promise", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = filter(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return Promise.resolve(value % 2 === 0);
+        },
+      );
+      const expected = [2, 4];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("without promise", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = filter([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return value % 2 === 0;
+      });
+      const expected = [2, 4];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with promise", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = filter([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return Promise.resolve(value % 2 === 0);
+      });
+      const expected = [2, 4];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/find.ts b/async/find.ts
new file mode 100644
index 0000000..03b0426
--- /dev/null
+++ b/async/find.ts
@@ -0,0 +1,28 @@
+/**
+ * Returns the first element in the iterable that satisfies the provided
+ * testing function. Otherwise, undefined is returned.
+ *
+ * @param iterable The iterable to search.
+ * @param fn The function to test with.
+ * @returns The first element that satisfies the provided testing function.
+ *
+ * @example
+ * ```ts
+ * import { find } from "@core/iterutil/async/find";
+ *
+ * const value = await find([1, 2, 3, 4, 5], (value) => value % 2 === 0);
+ * console.log(value); // 2
+ * ```
+ */
+export async function find<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T, index: number) => boolean | Promise<boolean>,
+): Promise<T | undefined> {
+  let index = 0;
+  for await (const value of iterable) {
+    if (await fn(value, index++)) {
+      return value;
+    }
+  }
+  return undefined;
+}
diff --git a/async/find_test.ts b/async/find_test.ts
new file mode 100644
index 0000000..d741de8
--- /dev/null
+++ b/async/find_test.ts
@@ -0,0 +1,90 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { find } from "./find.ts";
+
+Deno.test("find", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("found", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await find(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return value % 2 === 0;
+        },
+      );
+      const expected = 2;
+      assertEquals(result, expected);
+      assertEquals(values, [1, 2]);
+      assertEquals(indices, [0, 1]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("promise found", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await find(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return Promise.resolve(value % 2 === 0);
+        },
+      );
+      const expected = 2;
+      assertEquals(result, expected);
+      assertEquals(values, [1, 2]);
+      assertEquals(indices, [0, 1]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("not found", async () => {
+      const result = await find(toAsyncIterable([1, 2, 3, 4, 5]), () => false);
+      const expected = undefined;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("found", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await find([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return value % 2 === 0;
+      });
+      const expected = 2;
+      assertEquals(result, expected);
+      assertEquals(values, [1, 2]);
+      assertEquals(indices, [0, 1]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("promise found", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await find([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return Promise.resolve(value % 2 === 0);
+      });
+      const expected = 2;
+      assertEquals(result, expected);
+      assertEquals(values, [1, 2]);
+      assertEquals(indices, [0, 1]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("not found", async () => {
+      const result = await find([1, 2, 3, 4, 5], () => false);
+      const expected = undefined;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+});
diff --git a/async/first.ts b/async/first.ts
new file mode 100644
index 0000000..831c8aa
--- /dev/null
+++ b/async/first.ts
@@ -0,0 +1,23 @@
+/**
+ * Returns the first element of an iterable.
+ * If the iterable is empty, returns `undefined`.
+ *
+ * @param iterable The iterable to get the first element from.
+ * @returns The first element of the iterable, or `undefined` if the iterable is empty.
+ *
+ * @example
+ * ```ts
+ * import { first } from "@core/iterutil/async/first";
+ *
+ * const value = await first([1, 2, 3]);
+ * console.log(value); // 1
+ * ```
+ */
+export async function first<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): Promise<T | undefined> {
+  for await (const value of iterable) {
+    return value;
+  }
+  return undefined;
+}
diff --git a/async/first_test.ts b/async/first_test.ts
new file mode 100644
index 0000000..6163f9e
--- /dev/null
+++ b/async/first_test.ts
@@ -0,0 +1,38 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { first } from "./first.ts";
+
+Deno.test("first", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = await first(toAsyncIterable([1, 2, 3, 4, 5]));
+      const expected = 1;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = await first(toAsyncIterable([] as number[]));
+      const expected = undefined;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = await first([1, 2, 3, 4, 5]);
+      const expected = 1;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = await first([] as number[]);
+      const expected = undefined;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+});
diff --git a/async/flat_map.ts b/async/flat_map.ts
new file mode 100644
index 0000000..15c3e0b
--- /dev/null
+++ b/async/flat_map.ts
@@ -0,0 +1,30 @@
+/**
+ * Maps each value in an iterable to an iterable, then flattens the result.
+ *
+ * @param iterable The iterable to flat map.
+ * @param fn The function to map with.
+ * @returns The flat mapped iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { flatMap } from "@core/iterutil/async/flat-map";
+ *
+ * const iter = flatMap([1, 2, 3], (value) => [value, value]);
+ * console.log(await toArray(iter)); // [1, 1, 2, 2, 3, 3]
+ * ```
+ */
+export async function* flatMap<T, U>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (
+    value: T,
+    index: number,
+  ) => Iterable<U> | AsyncIterable<U> | Promise<Iterable<U>>,
+): AsyncIterable<U> {
+  let index = 0;
+  for await (const value of iterable) {
+    for await (const item of await fn(value, index++)) {
+      yield item;
+    }
+  }
+}
diff --git a/async/flat_map_test.ts b/async/flat_map_test.ts
new file mode 100644
index 0000000..9ad312d
--- /dev/null
+++ b/async/flat_map_test.ts
@@ -0,0 +1,124 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { flatMap } from "./flat_map.ts";
+
+Deno.test("flatMap", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("single nest", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = flatMap(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return [value, value];
+        },
+      );
+      const expected = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("single async iterable nest", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = flatMap(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return toAsyncIterable([value, value]);
+        },
+      );
+      const expected = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("single promise nest", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = flatMap(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return Promise.resolve([value, value]);
+        },
+      );
+      const expected = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("multi nest", async () => {
+      const result = flatMap(toAsyncIterable([1, 2, 3, 4, 5]), (v) => [[v, v]]);
+      const expected = [[1, 1], [2, 2], [3, 3], [4, 4], [5, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("single nest", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = flatMap([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return [value, value];
+      });
+      const expected = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("single async iterable nest", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = flatMap([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return toAsyncIterable([value, value]);
+      });
+      const expected = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("single promise nest", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = flatMap([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return Promise.resolve([value, value]);
+      });
+      const expected = [1, 1, 2, 2, 3, 3, 4, 4, 5, 5];
+      assertEquals(await toArray(result), expected);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("multi nest", async () => {
+      const result = flatMap([1, 2, 3, 4, 5], (v) => [[v, v]]);
+      const expected = [[1, 1], [2, 2], [3, 3], [4, 4], [5, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+  });
+});
diff --git a/async/flatten.ts b/async/flatten.ts
new file mode 100644
index 0000000..d33fe0e
--- /dev/null
+++ b/async/flatten.ts
@@ -0,0 +1,26 @@
+/**
+ * Flattens an iterable of iterables into a single iterable.
+ *
+ * @param iterable The iterable to flatten.
+ * @returns The flattened iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { flatten } from "@core/iterutil/async/flatten";
+ *
+ * const iter = flatten([[1, 2], [3, 4], [5]]);
+ * console.log(await toArray(iter)); // [1, 2, 3, 4, 5]
+ * ```
+ */
+export async function* flatten<T>(
+  iterable:
+    | Iterable<Iterable<T> | AsyncIterable<T> | Promise<Iterable<T>>>
+    | AsyncIterable<Iterable<T> | AsyncIterable<T> | Promise<Iterable<T>>>,
+): AsyncIterable<T> {
+  for await (const innerIterable of iterable) {
+    for await (const value of innerIterable) {
+      yield value;
+    }
+  }
+}
diff --git a/async/flatten_test.ts b/async/flatten_test.ts
new file mode 100644
index 0000000..376b0ef
--- /dev/null
+++ b/async/flatten_test.ts
@@ -0,0 +1,45 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { flatten } from "./flatten.ts";
+
+Deno.test("flatten", async (t) => {
+  await t.step("with iterable", async (t) => {
+    await t.step("single nest", async () => {
+      const result = flatten([[1, 2], [3, 4], [5]]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("single async iterable nest", async () => {
+      const result = flatten([
+        toAsyncIterable([1, 2]),
+        toAsyncIterable([3, 4]),
+        toAsyncIterable([5]),
+      ]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("single promise nest", async () => {
+      const result = flatten<number>([
+        Promise.resolve([1, 2]),
+        Promise.resolve([3, 4]),
+        Promise.resolve([5]),
+      ]);
+      const expected = [1, 2, 3, 4, 5];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("multi nest", async () => {
+      const result = flatten([[[1, 2], [3, 4]], [[5]]]);
+      const expected = [[1, 2], [3, 4], [5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number[]>>>(true);
+    });
+  });
+});
diff --git a/async/for_each.ts b/async/for_each.ts
new file mode 100644
index 0000000..fb78a2c
--- /dev/null
+++ b/async/for_each.ts
@@ -0,0 +1,23 @@
+/**
+ * Calls a function for each value in an iterable.
+ *
+ * @param iterable The iterable to iterate over.
+ * @param fn The function to call for each value.
+ *
+ * @example
+ * ```ts
+ * import { forEach } from "@core/iterutil/async/for-each";
+ * await forEach([1, 2, 3], console.log);
+ * // 1
+ * // 2
+ * // 3
+ */
+export async function forEach<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T, index: number) => void | Promise<void>,
+): Promise<void> {
+  let index = 0;
+  for await (const value of iterable) {
+    await fn(value, index++);
+  }
+}
diff --git a/async/for_each_test.ts b/async/for_each_test.ts
new file mode 100644
index 0000000..a8402ab
--- /dev/null
+++ b/async/for_each_test.ts
@@ -0,0 +1,51 @@
+import { assertEquals } from "@std/assert";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { forEach } from "./for_each.ts";
+
+Deno.test("forEach", async (t) => {
+  await t.step("with async iterable", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    await forEach(toAsyncIterable([1, 2, 3, 4, 5]), (value, index) => {
+      values.push(value);
+      indices.push(index);
+    });
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+  });
+
+  await t.step("with async iterable (promise)", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    await forEach(toAsyncIterable([1, 2, 3, 4, 5]), (value, index) => {
+      values.push(value);
+      indices.push(index);
+      return Promise.resolve();
+    });
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+  });
+
+  await t.step("with iterable", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    await forEach([1, 2, 3, 4, 5], (value, index) => {
+      values.push(value);
+      indices.push(index);
+    });
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+  });
+
+  await t.step("with iterable (promise)", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    await forEach([1, 2, 3, 4, 5], (value, index) => {
+      values.push(value);
+      indices.push(index);
+      return Promise.resolve();
+    });
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+  });
+});
diff --git a/async/iter.ts b/async/iter.ts
new file mode 100644
index 0000000..633363b
--- /dev/null
+++ b/async/iter.ts
@@ -0,0 +1,34 @@
+/**
+ * Convert an iterable to an iterator.
+ *
+ * @param iterable The iterable to convert.
+ * @returns The iterator.
+ *
+ * @example
+ * ```ts
+ * import { iter } from "@core/iterutil/async/iter";
+ *
+ * const it = iter([1, 2, 3, 4, 5]);
+ * console.log(await it.next()); // { value: 1, done: false }
+ * console.log(await it.next()); // { value: 2, done: false }
+ *
+ * for await (const value of it) {
+ *   console.log(value);
+ * }
+ * // 3
+ * // 4
+ * // 5
+ * ```
+ */
+export function iter<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): AsyncIterableIterator<T> {
+  const inner = Symbol.iterator in iterable
+    ? iterable[Symbol.iterator]()
+    : iterable[Symbol.asyncIterator]();
+  const it = {
+    next: async () => await inner.next(),
+    [Symbol.asyncIterator]: () => it,
+  };
+  return it;
+}
diff --git a/async/iter_test.ts b/async/iter_test.ts
new file mode 100644
index 0000000..b995602
--- /dev/null
+++ b/async/iter_test.ts
@@ -0,0 +1,23 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { iter } from "./iter.ts";
+
+Deno.test("iter", async (t) => {
+  await t.step("with async iterable", async () => {
+    const it = iter(toAsyncIterable([0, 1, 2, 3, 4, 5]));
+    assertEquals(await it.next(), { done: false, value: 0 });
+    assertEquals(await it.next(), { done: false, value: 1 });
+    assertEquals(await toArray(it), [2, 3, 4, 5]);
+    assertType<IsExact<typeof it, AsyncIterableIterator<number>>>(true);
+  });
+
+  await t.step("with iterable", async () => {
+    const it = iter([0, 1, 2, 3, 4, 5]);
+    assertEquals(await it.next(), { done: false, value: 0 });
+    assertEquals(await it.next(), { done: false, value: 1 });
+    assertEquals(await toArray(it), [2, 3, 4, 5]);
+    assertType<IsExact<typeof it, AsyncIterableIterator<number>>>(true);
+  });
+});
diff --git a/async/last.ts b/async/last.ts
new file mode 100644
index 0000000..4de6bb5
--- /dev/null
+++ b/async/last.ts
@@ -0,0 +1,23 @@
+/**
+ * Returns the last element of an iterable.
+ *
+ * @param iterable The iterable to get the last element of.
+ * @returns The last element of the iterable, or `undefined` if the iterable is empty.
+ *
+ * @example
+ * ```ts
+ * import { last } from "@core/iterutil/async/last";
+ *
+ * console.log(await last([1, 2, 3])); // 3
+ * console.log(await last([])); // undefined
+ * ```
+ */
+export async function last<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): Promise<T | undefined> {
+  let lastValue: T | undefined = undefined;
+  for await (const value of iterable) {
+    lastValue = value;
+  }
+  return lastValue;
+}
diff --git a/async/last_test.ts b/async/last_test.ts
new file mode 100644
index 0000000..0f32e5b
--- /dev/null
+++ b/async/last_test.ts
@@ -0,0 +1,38 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { last } from "./last.ts";
+
+Deno.test("last", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = await last(toAsyncIterable([1, 2, 3, 4, 5]));
+      const expected = 5;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = await last(toAsyncIterable([] as number[]));
+      const expected = undefined;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = await last([1, 2, 3, 4, 5]);
+      const expected = 5;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = await last([] as number[]);
+      const expected = undefined;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+});
diff --git a/async/map.ts b/async/map.ts
new file mode 100644
index 0000000..fc1f2a5
--- /dev/null
+++ b/async/map.ts
@@ -0,0 +1,25 @@
+/**
+ * Maps an iterable with a function.
+ *
+ * @param iterable The iterable to map.
+ * @param fn The function to map with.
+ * @returns The mapped iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { map } from "@core/iterutil/async/map";
+ *
+ * const iter = map([1, 2, 3], (value) => value * 2);
+ * console.log(await toArray(iter)); // [2, 4, 6]
+ * ```
+ */
+export async function* map<T, U>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T, index: number) => U | Promise<U>,
+): AsyncIterable<U> {
+  let index = 0;
+  for await (const value of iterable) {
+    yield await fn(value, index++);
+  }
+}
diff --git a/async/map_test.ts b/async/map_test.ts
new file mode 100644
index 0000000..12a8b02
--- /dev/null
+++ b/async/map_test.ts
@@ -0,0 +1,67 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { map } from "./map.ts";
+
+Deno.test("map", async (t) => {
+  await t.step("with async iterable", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    const result = map(toAsyncIterable([1, 2, 3, 4, 5]), (value, index) => {
+      values.push(value);
+      indices.push(index);
+      return value * 2;
+    });
+    const expected = [2, 4, 6, 8, 10];
+    assertEquals(await toArray(result), expected);
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+    assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+  });
+
+  await t.step("with iterable (promise)", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    const result = map(toAsyncIterable([1, 2, 3, 4, 5]), (value, index) => {
+      values.push(value);
+      indices.push(index);
+      return Promise.resolve(value * 2);
+    });
+    const expected = [2, 4, 6, 8, 10];
+    assertEquals(await toArray(result), expected);
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+    assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+  });
+
+  await t.step("with iterable", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    const result = map([1, 2, 3, 4, 5], (value, index) => {
+      values.push(value);
+      indices.push(index);
+      return value * 2;
+    });
+    const expected = [2, 4, 6, 8, 10];
+    assertEquals(await toArray(result), expected);
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+    assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+  });
+
+  await t.step("with iterable (promise)", async () => {
+    const values: number[] = [];
+    const indices: number[] = [];
+    const result = map([1, 2, 3, 4, 5], (value, index) => {
+      values.push(value);
+      indices.push(index);
+      return Promise.resolve(value * 2);
+    });
+    const expected = [2, 4, 6, 8, 10];
+    assertEquals(await toArray(result), expected);
+    assertEquals(values, [1, 2, 3, 4, 5]);
+    assertEquals(indices, [0, 1, 2, 3, 4]);
+    assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+  });
+});
diff --git a/async/mod.ts b/async/mod.ts
new file mode 100644
index 0000000..d99226c
--- /dev/null
+++ b/async/mod.ts
@@ -0,0 +1,28 @@
+export * from "./chain.ts";
+export * from "./chunked.ts";
+export * from "./compact.ts";
+export * from "./compress.ts";
+export * from "./cycle.ts";
+export * from "./drop.ts";
+export * from "./drop_while.ts";
+export * from "./enumerate.ts";
+export * from "./every.ts";
+export * from "./filter.ts";
+export * from "./find.ts";
+export * from "./first.ts";
+export * from "./flat_map.ts";
+export * from "./flatten.ts";
+export * from "./for_each.ts";
+export * from "./iter.ts";
+export * from "./last.ts";
+export * from "./map.ts";
+export * from "./pairwise.ts";
+export * from "./partition.ts";
+export * from "./reduce.ts";
+export * from "./some.ts";
+export * from "./take.ts";
+export * from "./take_while.ts";
+export * from "./to_array.ts";
+export * from "./to_async_iterable.ts";
+export * from "./uniq.ts";
+export * from "./zip.ts";
diff --git a/async/mod_test.ts b/async/mod_test.ts
new file mode 100644
index 0000000..3409c34
--- /dev/null
+++ b/async/mod_test.ts
@@ -0,0 +1,59 @@
+import { assertArrayIncludes } from "@std/assert";
+import { basename, globToRegExp, join } from "@std/path";
+import { ensure, is } from "@core/unknownutil";
+import { parse } from "@std/jsonc";
+
+const excludes = [
+  "mod.ts",
+  "*_test.ts",
+  "*_bench.ts",
+];
+
+Deno.test("mod.ts must exports all exports in public modules", async () => {
+  const modExports = await listModExports("./mod.ts");
+  const pubExports = [];
+  for await (const name of iterPublicModules(".")) {
+    pubExports.push(...await listModExports(`./${name}.ts`));
+  }
+  assertArrayIncludes(modExports, pubExports);
+});
+
+Deno.test("JSR exports must have all exports in mod.ts", async () => {
+  const jsrExportEntries = await listJsrExportEntries();
+  const modExportEntries: [string, string][] = [];
+  for await (const name of iterPublicModules(".")) {
+    modExportEntries.push([
+      `./async/${name.replaceAll("_", "-")}`,
+      `./async/${name}.ts`,
+    ]);
+  }
+  assertArrayIncludes(jsrExportEntries, modExportEntries);
+});
+
+async function* iterPublicModules(relpath: string): AsyncIterable<string> {
+  const patterns = excludes.map((p) => globToRegExp(p));
+  const root = join(import.meta.dirname!, relpath);
+  for await (const entry of Deno.readDir(root)) {
+    if (!entry.isFile || !entry.name.endsWith(".ts")) continue;
+    if (patterns.some((p) => p.test(entry.name))) continue;
+    yield basename(entry.name, ".ts");
+  }
+}
+
+async function listModExports(path: string): Promise<string[]> {
+  const mod = await import(import.meta.resolve(path));
+  return [...Object.keys(mod)];
+}
+
+async function listJsrExportEntries(): Promise<[string, string][]> {
+  const text = await Deno.readTextFile(
+    new URL(import.meta.resolve("../deno.jsonc")),
+  );
+  const json = ensure(
+    parse(text),
+    is.ObjectOf({
+      exports: is.RecordOf(is.String, is.String),
+    }),
+  );
+  return Object.entries(json.exports);
+}
diff --git a/async/pairwise.ts b/async/pairwise.ts
new file mode 100644
index 0000000..85499d3
--- /dev/null
+++ b/async/pairwise.ts
@@ -0,0 +1,34 @@
+/**
+ * Returns an iterable that pairs adjacent elements from the input iterable.
+ *
+ * When the input iterable has a finite number of items `n`, the output iterable will have `n - 1` items.
+ *
+ * @param iterable The iterable to pair elements from.
+ * @returns The paired iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { pairwise } from "@core/iterutil/async/pairwise";
+ *
+ * const iter = pairwise([1, 2, 3, 4, 5]);
+ * console.log(await toArray(iter)); // [[1, 2], [2, 3], [3, 4], [4, 5]]
+ * ```
+ */
+export async function* pairwise<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): AsyncIterable<[T, T]> {
+  const it = Symbol.iterator in iterable
+    ? iterable[Symbol.iterator]()
+    : iterable[Symbol.asyncIterator]();
+  let result = await it.next();
+  while (!result.done) {
+    const first = result.value;
+    result = await it.next();
+    if (result.done) {
+      break;
+    }
+    const second = result.value;
+    yield [first, second];
+  }
+}
diff --git a/async/pairwise_test.ts b/async/pairwise_test.ts
new file mode 100644
index 0000000..892d28c
--- /dev/null
+++ b/async/pairwise_test.ts
@@ -0,0 +1,53 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { pairwise } from "./pairwise.ts";
+
+Deno.test("pairwise", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = pairwise(toAsyncIterable([1, 2, 3, 4, 5]));
+      const expected = [[1, 2], [2, 3], [3, 4], [4, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with single value iterable", async () => {
+      const result = pairwise(toAsyncIterable([1]));
+      const expected: number[][] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = pairwise(toAsyncIterable([] as number[]));
+      const expected: number[][] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const result = pairwise([1, 2, 3, 4, 5]);
+      const expected = [[1, 2], [2, 3], [3, 4], [4, 5]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with single value iterable", async () => {
+      const result = pairwise([1]);
+      const expected: number[][] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const result = pairwise([] as number[]);
+      const expected: number[][] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, number]>>>(true);
+    });
+  });
+});
diff --git a/async/partition.ts b/async/partition.ts
new file mode 100644
index 0000000..35ea1b4
--- /dev/null
+++ b/async/partition.ts
@@ -0,0 +1,31 @@
+/**
+ * Partitions an iterable into two arrays based on a selector function.
+ *
+ * @param iterable The iterable to partition.
+ * @param selector The function to partition with.
+ * @returns The partitioned arrays.
+ *
+ * @example
+ * ```ts
+ * import { partition } from "@core/iterutil/partition";
+ *
+ * const [even, odd] = await partition([1, 2, 3, 4, 5], (value) => value % 2 === 0);
+ * console.log(even); // [2, 4]
+ * console.log(odd); // [1, 3, 5]
+ * ```
+ */
+export async function partition<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  selector: (value: T, index: number) => boolean | Promise<boolean>,
+): Promise<[T[], T[]]> {
+  let index = 0;
+  const [a, b]: [T[], T[]] = [[], []];
+  for await (const value of iterable) {
+    if (await selector(value, index++)) {
+      a.push(value);
+    } else {
+      b.push(value);
+    }
+  }
+  return [a, b];
+}
diff --git a/async/partition_test.ts b/async/partition_test.ts
new file mode 100644
index 0000000..9d13ff2
--- /dev/null
+++ b/async/partition_test.ts
@@ -0,0 +1,99 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { partition } from "./partition.ts";
+
+Deno.test("partition", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const [left, right] = await partition(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return value % 2 === 0;
+        },
+      );
+      assertEquals(left, [2, 4]);
+      assertEquals(right, [1, 3, 5]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof left, number[]>>(true);
+      assertType<IsExact<typeof right, number[]>>(true);
+    });
+
+    await t.step("with non empty iterable (promise)", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const [left, right] = await partition(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (value, index) => {
+          values.push(value);
+          indices.push(index);
+          return Promise.resolve(value % 2 === 0);
+        },
+      );
+      assertEquals(left, [2, 4]);
+      assertEquals(right, [1, 3, 5]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof left, number[]>>(true);
+      assertType<IsExact<typeof right, number[]>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const [left, right] = await partition(
+        toAsyncIterable([] as number[]),
+        (v) => v % 2 === 0,
+      );
+      assertEquals(left, []);
+      assertEquals(right, []);
+      assertType<IsExact<typeof left, number[]>>(true);
+      assertType<IsExact<typeof right, number[]>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with non empty iterable", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const [left, right] = await partition([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return value % 2 === 0;
+      });
+      assertEquals(left, [2, 4]);
+      assertEquals(right, [1, 3, 5]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof left, number[]>>(true);
+      assertType<IsExact<typeof right, number[]>>(true);
+    });
+
+    await t.step("with non empty iterable (promise)", async () => {
+      const values: number[] = [];
+      const indices: number[] = [];
+      const [left, right] = await partition([1, 2, 3, 4, 5], (value, index) => {
+        values.push(value);
+        indices.push(index);
+        return Promise.resolve(value % 2 === 0);
+      });
+      assertEquals(left, [2, 4]);
+      assertEquals(right, [1, 3, 5]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof left, number[]>>(true);
+      assertType<IsExact<typeof right, number[]>>(true);
+    });
+
+    await t.step("with empty iterable", async () => {
+      const [left, right] = await partition([] as number[], (v) => v % 2 === 0);
+      assertEquals(left, []);
+      assertEquals(right, []);
+      assertType<IsExact<typeof left, number[]>>(true);
+      assertType<IsExact<typeof right, number[]>>(true);
+    });
+  });
+});
diff --git a/async/reduce.ts b/async/reduce.ts
new file mode 100644
index 0000000..86fc2d9
--- /dev/null
+++ b/async/reduce.ts
@@ -0,0 +1,69 @@
+/**
+ * Reduces an iterable into a single value.
+ *
+ * @param iterable The iterable to reduce.
+ * @param fn The function to reduce with.
+ * @returns The reduced value.
+ *
+ * @example
+ * ```ts
+ * import { reduce } from "@core/iterutil/async/reduce";
+ *
+ * const sum = await reduce([1, 2, 3, 4, 5], (acc, value) => acc + value);
+ * console.log(sum); // 15
+ * ```
+ */
+export function reduce<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (acc: T, value: T, index: number) => T | Promise<T>,
+): Promise<T | undefined>;
+
+/**
+ * Reduces an iterable into a single value.
+ *
+ * @param iterable The iterable to reduce.
+ * @param fn The function to reduce with.
+ * @param initial The initial value to start reducing with.
+ * @returns The reduced value.
+ *
+ * @example
+ * ```ts
+ * import { reduce } from "@core/iterutil/async/reduce";
+ *
+ * const joined = await reduce([1, 2, 3, 4, 5], (acc, value) => acc + value.toString(), "");
+ * console.log(joined); // 12345
+ * ```
+ */
+export function reduce<T, U>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (acc: U, value: T, index: number) => U | Promise<U>,
+  initial: U,
+): Promise<U>;
+
+export async function reduce<T, U = T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (acc: U, value: T, index: number) => U | Promise<U>,
+  initial?: U,
+): Promise<U | undefined> {
+  const it = Symbol.iterator in iterable
+    ? iterable[Symbol.iterator]()
+    : iterable[Symbol.asyncIterator]();
+  let index = 0;
+  if (initial == null) {
+    const { done, value } = await it.next();
+    if (done) {
+      return undefined;
+    }
+    initial = value as unknown as U;
+    index = 1;
+  }
+  let acc: U = initial;
+  while (true) {
+    const { done, value } = await it.next();
+    if (done) {
+      break;
+    }
+    acc = await fn(acc, value as T, index++);
+  }
+  return acc;
+}
diff --git a/async/reduce_test.ts b/async/reduce_test.ts
new file mode 100644
index 0000000..fa3628e
--- /dev/null
+++ b/async/reduce_test.ts
@@ -0,0 +1,175 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { reduce } from "./reduce.ts";
+
+Deno.test("reduce", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with initial", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (acc, value, index) => {
+          accumulators.push(acc);
+          values.push(value);
+          indices.push(index);
+          return acc + value;
+        },
+        5,
+      );
+      assertEquals(result, 20);
+      assertEquals(accumulators, [5, 6, 8, 11, 15]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number>>(true);
+    });
+
+    await t.step("with initial promise", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (acc, value, index) => {
+          accumulators.push(acc);
+          values.push(value);
+          indices.push(index);
+          return Promise.resolve(acc + value);
+        },
+        5,
+      );
+      assertEquals(result, 20);
+      assertEquals(accumulators, [5, 6, 8, 11, 15]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number>>(true);
+    });
+
+    await t.step("without initial", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (acc, value, index) => {
+          accumulators.push(acc);
+          values.push(value);
+          indices.push(index);
+          return acc + value;
+        },
+      );
+      assertEquals(result, 15);
+      assertEquals(accumulators, [1, 3, 6, 10]);
+      assertEquals(values, [2, 3, 4, 5]);
+      assertEquals(indices, [1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("without initial promise", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        (acc, value, index) => {
+          accumulators.push(acc);
+          values.push(value);
+          indices.push(index);
+          return Promise.resolve(acc + value);
+        },
+      );
+      assertEquals(result, 15);
+      assertEquals(accumulators, [1, 3, 6, 10]);
+      assertEquals(values, [2, 3, 4, 5]);
+      assertEquals(indices, [1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("without initial / with empty iterable", async () => {
+      const result = await reduce(
+        toAsyncIterable([] as number[]),
+        (acc, v) => acc + v,
+      );
+      assertEquals(result, undefined);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with initial", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce([1, 2, 3, 4, 5], (acc, value, index) => {
+        accumulators.push(acc);
+        values.push(value);
+        indices.push(index);
+        return acc + value;
+      }, 5);
+      assertEquals(result, 20);
+      assertEquals(accumulators, [5, 6, 8, 11, 15]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number>>(true);
+    });
+
+    await t.step("with initial promise", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce([1, 2, 3, 4, 5], (acc, value, index) => {
+        accumulators.push(acc);
+        values.push(value);
+        indices.push(index);
+        return Promise.resolve(acc + value);
+      }, 5);
+      assertEquals(result, 20);
+      assertEquals(accumulators, [5, 6, 8, 11, 15]);
+      assertEquals(values, [1, 2, 3, 4, 5]);
+      assertEquals(indices, [0, 1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number>>(true);
+    });
+
+    await t.step("without initial", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce([1, 2, 3, 4, 5], (acc, value, index) => {
+        accumulators.push(acc);
+        values.push(value);
+        indices.push(index);
+        return acc + value;
+      });
+      assertEquals(result, 15);
+      assertEquals(accumulators, [1, 3, 6, 10]);
+      assertEquals(values, [2, 3, 4, 5]);
+      assertEquals(indices, [1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("without initial promise", async () => {
+      const accumulators: number[] = [];
+      const values: number[] = [];
+      const indices: number[] = [];
+      const result = await reduce([1, 2, 3, 4, 5], (acc, value, index) => {
+        accumulators.push(acc);
+        values.push(value);
+        indices.push(index);
+        return Promise.resolve(acc + value);
+      });
+      assertEquals(result, 15);
+      assertEquals(accumulators, [1, 3, 6, 10]);
+      assertEquals(values, [2, 3, 4, 5]);
+      assertEquals(indices, [1, 2, 3, 4]);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+
+    await t.step("without initial / with empty iterable", async () => {
+      const result = await reduce([] as number[], (acc, v) => acc + v);
+      assertEquals(result, undefined);
+      assertType<IsExact<typeof result, number | undefined>>(true);
+    });
+  });
+});
diff --git a/async/some.ts b/async/some.ts
new file mode 100644
index 0000000..1cab821
--- /dev/null
+++ b/async/some.ts
@@ -0,0 +1,26 @@
+/**
+ * Returns true if at least one element in the iterable satisfies the provided
+ *
+ * @param iterable The iterable to check.
+ * @param fn The function to check with.
+ * @returns True if at least one element satisfies the provided function.
+ *
+ * @example
+ * ```ts
+ * import { some } from "@core/iterutil/async/some";
+ *
+ * console.log(await some([1, 2, 3], (value) => value % 2 === 0)); // true
+ * console.log(await some([1, 3, 5], (value) => value % 2 === 0)); // false
+ * ```
+ */
+export async function some<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T) => boolean | Promise<boolean>,
+): Promise<boolean> {
+  for await (const value of iterable) {
+    if (await fn(value)) {
+      return true;
+    }
+  }
+  return false;
+}
diff --git a/async/some_test.ts b/async/some_test.ts
new file mode 100644
index 0000000..16c1687
--- /dev/null
+++ b/async/some_test.ts
@@ -0,0 +1,38 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { some } from "./some.ts";
+
+Deno.test("some", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("true", async () => {
+      const result = await some(toAsyncIterable([1, 2, 3, 4, 5]), (v) => v > 4);
+      const expected = true;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("false", async () => {
+      const result = await some(toAsyncIterable([1, 2, 3, 4, 5]), (v) => v > 5);
+      const expected = false;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("true", async () => {
+      const result = await some([1, 2, 3, 4, 5], (v) => v > 4);
+      const expected = true;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+
+    await t.step("false", async () => {
+      const result = await some([1, 2, 3, 4, 5], (v) => v > 5);
+      const expected = false;
+      assertEquals(result, expected);
+      assertType<IsExact<typeof result, boolean>>(true);
+    });
+  });
+});
diff --git a/async/take.ts b/async/take.ts
new file mode 100644
index 0000000..6ee014d
--- /dev/null
+++ b/async/take.ts
@@ -0,0 +1,37 @@
+/**
+ * Take the first `limit` items from the iterable.
+ *
+ * It throws an error if `limit` is less than 0.
+ *
+ * @param iterable The iterable to take items from.
+ * @param limit The number of items to take.
+ * @returns The iterable with the first `limit` items taken.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { take } from "@core/iterutil/async/take";
+ *
+ * const iter = take([1, 2, 3, 4, 5], 2);
+ * console.log(await toArray(iter)); // [1, 2]
+ * ```
+ */
+export function take<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  limit: number,
+): AsyncIterable<T> {
+  if (limit < 0) {
+    throw new Error(
+      `limit argument must be greater than or equal to 0, but got ${limit}.`,
+    );
+  }
+  return async function* () {
+    let i = 0;
+    for await (const item of iterable) {
+      if (i++ >= limit) {
+        break;
+      }
+      yield item;
+    }
+  }();
+}
diff --git a/async/take_test.ts b/async/take_test.ts
new file mode 100644
index 0000000..1d0752e
--- /dev/null
+++ b/async/take_test.ts
@@ -0,0 +1,59 @@
+import { assertEquals, assertThrows } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { take } from "./take.ts";
+
+Deno.test("take", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with positive limit", async () => {
+      const result = take(toAsyncIterable([0, 1, 2, 3, 4]), 2);
+      const expected = [0, 1];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with negative limit", () => {
+      assertThrows(
+        () => {
+          take([0, 1, 2, 3, 4], -2);
+        },
+        Error,
+        "limit argument must be greater than or equal to 0, but got -2.",
+      );
+    });
+
+    await t.step("with 0 limit", async () => {
+      const result = take(toAsyncIterable([0, 1, 2, 3, 4]), 0);
+      const expected: number[] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with positive limit", async () => {
+      const result = take([0, 1, 2, 3, 4], 2);
+      const expected = [0, 1];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with negative limit", () => {
+      assertThrows(
+        () => {
+          take([0, 1, 2, 3, 4], -2);
+        },
+        Error,
+        "limit argument must be greater than or equal to 0, but got -2.",
+      );
+    });
+
+    await t.step("with 0 limit", async () => {
+      const result = take([0, 1, 2, 3, 4], 0);
+      const expected: number[] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/take_while.ts b/async/take_while.ts
new file mode 100644
index 0000000..07bd64f
--- /dev/null
+++ b/async/take_while.ts
@@ -0,0 +1,28 @@
+/**
+ * Take elements from the iterable while the predicate is true.
+ *
+ * @param iterable The iterable to take elements from.
+ * @param fn The predicate to take elements with.
+ * @returns The taken iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { takeWhile } from "@core/iterutil/async/take-while";
+ *
+ * const iter = takeWhile([1, 2, 3, 4, 5], (value) => value < 4);
+ * console.log(await toArray(iter)); // [1, 2, 3]
+ * ```
+ */
+export async function* takeWhile<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  fn: (value: T, index: number) => boolean | Promise<boolean>,
+): AsyncIterable<T> {
+  let index = 0;
+  for await (const value of iterable) {
+    if (!await fn(value, index++)) {
+      break;
+    }
+    yield value;
+  }
+}
diff --git a/async/take_while_test.ts b/async/take_while_test.ts
new file mode 100644
index 0000000..7377a83
--- /dev/null
+++ b/async/take_while_test.ts
@@ -0,0 +1,70 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { takeWhile } from "./take_while.ts";
+
+Deno.test("takeWhile", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("with some true", async () => {
+      const result = takeWhile(toAsyncIterable([0, 1, 2, 3, 4]), (v) => v < 2);
+      const expected = [0, 1];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with some promise true", async () => {
+      const result = takeWhile(
+        toAsyncIterable([0, 1, 2, 3, 4]),
+        (v) => Promise.resolve(v < 2),
+      );
+      const expected = [0, 1];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all true", async () => {
+      const result = takeWhile(toAsyncIterable([0, 1, 2, 3, 4]), () => true);
+      const expected = [0, 1, 2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all false", async () => {
+      const result = takeWhile(toAsyncIterable([0, 1, 2, 3, 4]), () => false);
+      const expected: number[] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("with some true", async () => {
+      const result = takeWhile([0, 1, 2, 3, 4], (v) => v < 2);
+      const expected = [0, 1];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with some promise true", async () => {
+      const result = takeWhile([0, 1, 2, 3, 4], (v) => Promise.resolve(v < 2));
+      const expected = [0, 1];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all true", async () => {
+      const result = takeWhile([0, 1, 2, 3, 4], () => true);
+      const expected = [0, 1, 2, 3, 4];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with all false", async () => {
+      const result = takeWhile([0, 1, 2, 3, 4], () => false);
+      const expected: number[] = [];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/to_array.ts b/async/to_array.ts
new file mode 100644
index 0000000..3d4adf8
--- /dev/null
+++ b/async/to_array.ts
@@ -0,0 +1,34 @@
+/**
+ * Converts an iterable or async iterable to an array.
+ *
+ * @param iterable The iterable or async iterable to convert.
+ * @returns The array.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ *
+ * const arr1 = await toArray(function*() {
+ *   yield 1;
+ *   yield 2;
+ *   yield 3;
+ * }());
+ * console.log(arr1); // [1, 2, 3]
+ *
+ * const arr2 = await toArray(async function*() {
+ *   yield 1;
+ *   yield 2;
+ *   yield 3;
+ * }());
+ * console.log(arr2); // [1, 2, 3]
+ * ```
+ */
+export async function toArray<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+): Promise<T[]> {
+  const result: T[] = [];
+  for await (const value of iterable) {
+    result.push(value);
+  }
+  return result;
+}
diff --git a/async/to_array_test.ts b/async/to_array_test.ts
new file mode 100644
index 0000000..a86807c
--- /dev/null
+++ b/async/to_array_test.ts
@@ -0,0 +1,27 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toArray } from "./to_array.ts";
+
+Deno.test("toArray", async (t) => {
+  await t.step("with async iterable", async () => {
+    const result = await toArray(async function* () {
+      yield 1 as number;
+      yield 2 as number;
+      yield 3 as number;
+    }());
+    const expected = [1, 2, 3];
+    assertEquals(result, expected);
+    assertType<IsExact<typeof result, number[]>>(true);
+  });
+
+  await t.step("with iterable", async () => {
+    const result = await toArray(function* () {
+      yield 1 as number;
+      yield 2 as number;
+      yield 3 as number;
+    }());
+    const expected = [1, 2, 3];
+    assertEquals(result, expected);
+    assertType<IsExact<typeof result, number[]>>(true);
+  });
+});
diff --git a/async/to_async_iterable.ts b/async/to_async_iterable.ts
new file mode 100644
index 0000000..a195860
--- /dev/null
+++ b/async/to_async_iterable.ts
@@ -0,0 +1,20 @@
+/**
+ * Converts an iterable to an async iterable.
+ *
+ * @param iterable The iterable to convert.
+ * @returns The async iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { toAsyncIterable } from "@core/iterutil/async/to-async-iterable";
+ *
+ * const iter = toAsyncIterable([1, 2, 3]);
+ * console.log(await toArray(iter)); // [1, 2, 3]
+ * ```
+ */
+export async function* toAsyncIterable<T>(
+  iterable: Iterable<T>,
+): AsyncIterable<T> {
+  yield* iterable;
+}
diff --git a/async/to_async_iterable_test.ts b/async/to_async_iterable_test.ts
new file mode 100644
index 0000000..a82f3d4
--- /dev/null
+++ b/async/to_async_iterable_test.ts
@@ -0,0 +1,11 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toArray } from "./to_array.ts";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+
+Deno.test("toAsyncIterable", async () => {
+  const result = toAsyncIterable([1, 2, 3, 4, 5]);
+  const expected = [1, 2, 3, 4, 5];
+  assertEquals(await toArray(result), expected);
+  assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+});
diff --git a/async/uniq.ts b/async/uniq.ts
new file mode 100644
index 0000000..cc6eb15
--- /dev/null
+++ b/async/uniq.ts
@@ -0,0 +1,41 @@
+/**
+ * Returns an iterable that yields the unique elements of the input iterable.
+ *
+ * @param iterable The iterable to get the unique elements of.
+ * @param identify An optional function to transform the elements before checking for uniqueness.
+ * @returns An iterable that yields the unique elements of the input iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { uniq } from "@core/iterutil/async/uniq";
+ *
+ * const iter = uniq([1, 2, 2, 3, 3, 3]);
+ * console.log(await toArray(iter)); // [1, 2, 3]
+ * ```
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { uniq } from "@core/iterutil/async/uniq";
+ *
+ * const iter = uniq(
+ *   [1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31],
+ *   (v) => Math.floor(v / 10),
+ * );
+ * console.log(await toArray(iter)); // [1, 10, 20, 30]
+ * ```
+ */
+export async function* uniq<T>(
+  iterable: Iterable<T> | AsyncIterable<T>,
+  identify: (v: T) => unknown | Promise<unknown> = (v) => v,
+): AsyncIterable<T> {
+  const set = new Set<unknown>();
+  for await (const item of iterable) {
+    const identity = await identify(item);
+    if (!set.has(identity)) {
+      set.add(identity);
+      yield item;
+    }
+  }
+}
diff --git a/async/uniq_test.ts b/async/uniq_test.ts
new file mode 100644
index 0000000..4ed8498
--- /dev/null
+++ b/async/uniq_test.ts
@@ -0,0 +1,67 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { uniq } from "./uniq.ts";
+
+Deno.test("uniq", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("default", async () => {
+      const result = uniq(
+        toAsyncIterable([1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31]),
+      );
+      const expected = [1, 2, 3, 10, 20, 30, 11, 21, 31];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with identify", async () => {
+      const result = uniq(
+        toAsyncIterable([1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31]),
+        (v) => Math.floor(v / 10),
+      );
+      const expected = [1, 10, 20, 30];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with identify promise", async () => {
+      const result = uniq(
+        toAsyncIterable([1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31]),
+        (v) => Promise.resolve(Math.floor(v / 10)),
+      );
+      const expected = [1, 10, 20, 30];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("default", async () => {
+      const result = uniq([1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31]);
+      const expected = [1, 2, 3, 10, 20, 30, 11, 21, 31];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with identify", async () => {
+      const result = uniq(
+        [1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31],
+        (v) => Math.floor(v / 10),
+      );
+      const expected = [1, 10, 20, 30];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+
+    await t.step("with identify promise", async () => {
+      const result = uniq(
+        [1, 2, 3, 1, 2, 3, 10, 20, 30, 11, 21, 31],
+        (v) => Promise.resolve(Math.floor(v / 10)),
+      );
+      const expected = [1, 10, 20, 30];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<number>>>(true);
+    });
+  });
+});
diff --git a/async/zip.ts b/async/zip.ts
new file mode 100644
index 0000000..474758e
--- /dev/null
+++ b/async/zip.ts
@@ -0,0 +1,39 @@
+/**
+ * Zips multiple iterables into a single iterable.
+ *
+ * @param iterables The iterables to zip.
+ * @returns The zipped iterable.
+ *
+ * @example
+ * ```ts
+ * import { toArray } from "@core/iterutil/async/to-array";
+ * import { zip } from "@core/iterutil/async/zip";
+ *
+ * const iter = zip([1, 2, 3], ["a", "b", "c"]);
+ * console.log(await toArray(iter)); // [[1, "a"], [2, "b"], [3, "c"]]
+ * ```
+ */
+export async function* zip<
+  U extends (Iterable<unknown> | AsyncIterable<unknown>)[],
+>(
+  ...iterables: U
+): AsyncIterable<Zip<U>> {
+  const its = iterables.map((iterable) =>
+    Symbol.iterator in iterable
+      ? iterable[Symbol.iterator]()
+      : iterable[Symbol.asyncIterator]()
+  );
+  while (true) {
+    const rs = await Promise.all(its.map((it) => it.next()));
+    if (rs.find(({ done }) => !!done)) {
+      break;
+    }
+    yield rs.map(({ value }) => value) as Zip<U>;
+  }
+}
+
+export type Zip<T extends (Iterable<unknown> | AsyncIterable<unknown>)[]> = {
+  [P in keyof T]: T[P] extends Iterable<infer U> ? U
+    : T[P] extends AsyncIterable<infer U> ? U
+    : never;
+};
diff --git a/async/zip_test.ts b/async/zip_test.ts
new file mode 100644
index 0000000..beb936d
--- /dev/null
+++ b/async/zip_test.ts
@@ -0,0 +1,97 @@
+import { assertEquals } from "@std/assert";
+import { assertType, type IsExact } from "@std/testing/types";
+import { toAsyncIterable } from "./to_async_iterable.ts";
+import { toArray } from "./to_array.ts";
+import { zip } from "./zip.ts";
+
+Deno.test("zip", async (t) => {
+  await t.step("with async iterable", async (t) => {
+    await t.step("zip with two iterables", async () => {
+      const result = zip(
+        toAsyncIterable([1, 2, 3]),
+        toAsyncIterable(["a", "b", "c"]),
+      );
+      const expected = [[1, "a"], [2, "b"], [3, "c"]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, string]>>>(true);
+    });
+
+    await t.step("zip with two in-balanced iterables", async () => {
+      const result = zip(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        toAsyncIterable(["a", "b", "c"]),
+      );
+      const expected = [[1, "a"], [2, "b"], [3, "c"]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, string]>>>(true);
+    });
+
+    await t.step("zip with three iterables", async () => {
+      const result = zip(
+        toAsyncIterable([1, 2, 3]),
+        toAsyncIterable(["a", "b", "c"]),
+        [true, false, true],
+      );
+      const expected = [[1, "a", true], [2, "b", false], [3, "c", true]];
+      assertEquals(await toArray(result), expected);
+      assertType<
+        IsExact<typeof result, AsyncIterable<[number, string, boolean]>>
+      >(
+        true,
+      );
+    });
+
+    await t.step("zip with three in-balanced iterables", async () => {
+      const result = zip(
+        toAsyncIterable([1, 2, 3, 4, 5]),
+        toAsyncIterable(["a", "b", "c"]),
+        [true, false, true],
+      );
+      const expected = [[1, "a", true], [2, "b", false], [3, "c", true]];
+      assertEquals(await toArray(result), expected);
+      assertType<
+        IsExact<typeof result, AsyncIterable<[number, string, boolean]>>
+      >(
+        true,
+      );
+    });
+  });
+
+  await t.step("with iterable", async (t) => {
+    await t.step("zip with two iterables", async () => {
+      const result = zip([1, 2, 3], ["a", "b", "c"]);
+      const expected = [[1, "a"], [2, "b"], [3, "c"]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, string]>>>(true);
+    });
+
+    await t.step("zip with two in-balanced iterables", async () => {
+      const result = zip([1, 2, 3, 4, 5], ["a", "b", "c"]);
+      const expected = [[1, "a"], [2, "b"], [3, "c"]];
+      assertEquals(await toArray(result), expected);
+      assertType<IsExact<typeof result, AsyncIterable<[number, string]>>>(true);
+    });
+
+    await t.step("zip with three iterables", async () => {
+      const result = zip([1, 2, 3], ["a", "b", "c"], [true, false, true]);
+      const expected = [[1, "a", true], [2, "b", false], [3, "c", true]];
+      assertEquals(await toArray(result), expected);
+      assertType<
+        IsExact<typeof result, AsyncIterable<[number, string, boolean]>>
+      >(
+        true,
+      );
+    });
+
+    await t.step("zip with three in-balanced iterables", async () => {
+      const result = zip([1, 2, 3, 4, 5], ["a", "b", "c"], [true, false, true]);
+      const expected = [[1, "a", true], [2, "b", false], [3, "c", true]];
+      assertEquals(await toArray(result), expected);
+      assertType<
+        IsExact<typeof result, AsyncIterable<[number, string, boolean]>>
+      >(
+        true,
+      );
+    });
+  });
+});
diff --git a/deno.jsonc b/deno.jsonc
index c2a18e9..b4c6f8e 100644
--- a/deno.jsonc
+++ b/deno.jsonc
@@ -3,6 +3,35 @@
   "version": "0.0.0",
   "exports": {
     ".": "./mod.ts",
+    "./async": "./async/mod.ts",
+    "./async/chain": "./async/chain.ts",
+    "./async/chunked": "./async/chunked.ts",
+    "./async/compact": "./async/compact.ts",
+    "./async/compress": "./async/compress.ts",
+    "./async/cycle": "./async/cycle.ts",
+    "./async/drop": "./async/drop.ts",
+    "./async/drop-while": "./async/drop_while.ts",
+    "./async/enumerate": "./async/enumerate.ts",
+    "./async/every": "./async/every.ts",
+    "./async/filter": "./async/filter.ts",
+    "./async/find": "./async/find.ts",
+    "./async/first": "./async/first.ts",
+    "./async/flat-map": "./async/flat_map.ts",
+    "./async/flatten": "./async/flatten.ts",
+    "./async/for-each": "./async/for_each.ts",
+    "./async/iter": "./async/iter.ts",
+    "./async/last": "./async/last.ts",
+    "./async/map": "./async/map.ts",
+    "./async/pairwise": "./async/pairwise.ts",
+    "./async/partition": "./async/partition.ts",
+    "./async/reduce": "./async/reduce.ts",
+    "./async/some": "./async/some.ts",
+    "./async/take": "./async/take.ts",
+    "./async/take-while": "./async/take_while.ts",
+    "./async/to-array": "./async/to_array.ts",
+    "./async/to-async-iterable": "./async/to_async_iterable.ts",
+    "./async/uniq": "./async/uniq.ts",
+    "./async/zip": "./async/zip.ts",
     "./chain": "./chain.ts",
     "./chunked": "./chunked.ts",
     "./compact": "./compact.ts",
@@ -50,6 +79,35 @@
   },
   "imports": {
     "@core/iterutil": "./mod.ts",
+    "@core/iterutil/async": "./async/mod.ts",
+    "@core/iterutil/async/chain": "./async/chain.ts",
+    "@core/iterutil/async/chunked": "./async/chunked.ts",
+    "@core/iterutil/async/compact": "./async/compact.ts",
+    "@core/iterutil/async/compress": "./async/compress.ts",
+    "@core/iterutil/async/cycle": "./async/cycle.ts",
+    "@core/iterutil/async/drop": "./async/drop.ts",
+    "@core/iterutil/async/drop-while": "./async/drop_while.ts",
+    "@core/iterutil/async/enumerate": "./async/enumerate.ts",
+    "@core/iterutil/async/every": "./async/every.ts",
+    "@core/iterutil/async/filter": "./async/filter.ts",
+    "@core/iterutil/async/find": "./async/find.ts",
+    "@core/iterutil/async/first": "./async/first.ts",
+    "@core/iterutil/async/flat-map": "./async/flat_map.ts",
+    "@core/iterutil/async/flatten": "./async/flatten.ts",
+    "@core/iterutil/async/for-each": "./async/for_each.ts",
+    "@core/iterutil/async/iter": "./async/iter.ts",
+    "@core/iterutil/async/last": "./async/last.ts",
+    "@core/iterutil/async/map": "./async/map.ts",
+    "@core/iterutil/async/pairwise": "./async/pairwise.ts",
+    "@core/iterutil/async/partition": "./async/partition.ts",
+    "@core/iterutil/async/reduce": "./async/reduce.ts",
+    "@core/iterutil/async/some": "./async/some.ts",
+    "@core/iterutil/async/take": "./async/take.ts",
+    "@core/iterutil/async/take-while": "./async/take_while.ts",
+    "@core/iterutil/async/to-array": "./async/to_array.ts",
+    "@core/iterutil/async/to-async-iterable": "./async/to_async_iterable.ts",
+    "@core/iterutil/async/uniq": "./async/uniq.ts",
+    "@core/iterutil/async/zip": "./async/zip.ts",
     "@core/iterutil/chain": "./chain.ts",
     "@core/iterutil/chunked": "./chunked.ts",
     "@core/iterutil/compact": "./compact.ts",