diff --git a/package-lock.json b/package-lock.json
index a5b4a8e..2dfc0e0 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,6 +9,7 @@
       "version": "1.0.0",
       "license": "ISC",
       "dependencies": {
+        "@isaacs/ttlcache": "^1.4.1",
         "cors": "^2.8.5",
         "dotenv": "^16.4.5",
         "express": "^4.18.3",
@@ -58,6 +59,14 @@
         "node": ">=12"
       }
     },
+    "node_modules/@isaacs/ttlcache": {
+      "version": "1.4.1",
+      "resolved": "https://registry.npmjs.org/@isaacs/ttlcache/-/ttlcache-1.4.1.tgz",
+      "integrity": "sha512-RQgQ4uQ+pLbqXfOmieB91ejmLwvSgv9nLx6sT6sD83s7umBypgg+OIBOBbEUiJXrfpnp9j0mRhYYdzp9uqq3lA==",
+      "engines": {
+        "node": ">=12"
+      }
+    },
     "node_modules/@jridgewell/resolve-uri": {
       "version": "3.1.2",
       "resolved": "https://registry.npmjs.org/@jridgewell/resolve-uri/-/resolve-uri-3.1.2.tgz",
diff --git a/package.json b/package.json
index cf290e4..7f031c7 100644
--- a/package.json
+++ b/package.json
@@ -20,6 +20,7 @@
   },
   "homepage": "https://github.com/senacor/chatbot-poc-backend#readme",
   "dependencies": {
+    "@isaacs/ttlcache": "^1.4.1",
     "cors": "^2.8.5",
     "dotenv": "^16.4.5",
     "express": "^4.18.3",
diff --git a/src/chat/get-init.ts b/src/chat/get-init.ts
index 268192b..660dfee 100644
--- a/src/chat/get-init.ts
+++ b/src/chat/get-init.ts
@@ -1,12 +1,15 @@
 import { z } from "zod";
 import { makeGetEndpoint } from "../middleware/validation/makeGetEndpoint.js";
+import { addMessages, getUserVisibleMessages } from "../util/messageStore.js";
+import { IDENTITY_HEADER } from "./index.js";
 
 //TODO: Rework type inference of fileReader
 export const init = makeGetEndpoint(z.any(), async (_request, response) => {
-
-    return response
-        .status(200)
-        .send([
+    const identity = _request.header(IDENTITY_HEADER);
+    if (!identity) {
+        return response.status(400).send(`Missing ${IDENTITY_HEADER} header.`)
+    }
+    addMessages(identity, [
         {
             role: 'system',
             content: "Ask the user to provide the content of the file they want to chat about. Talk only about the content of the provided file."
@@ -16,4 +19,7 @@ export const init = makeGetEndpoint(z.any(), async (_request, response) => {
             content: "Hallo! Bitte laden Sie die Datei hoch, über die Sie chatten möchten."
         }
     ]);
+    return response
+        .status(200)
+        .send(getUserVisibleMessages(identity));
 });
\ No newline at end of file
diff --git a/src/chat/index.ts b/src/chat/index.ts
index 3ddef1a..e40175e 100644
--- a/src/chat/index.ts
+++ b/src/chat/index.ts
@@ -12,6 +12,7 @@ import fileUpload from "./upload-file.js";
 const PROMPT_FILE_NAME = "Prompt_Baufinanzierung.docx"
 const OPENAI_MODEL: ChatCompletionCreateParamsBase["model"] = "gpt-3.5-turbo";
 const RESPONSE_FORMAT: ChatCompletionCreateParams.ResponseFormat = {type: "text"};
+const IDENTITY_HEADER = 'X-Identity';
 
 
 const chatRouter = express.Router();
@@ -29,6 +30,7 @@ export {
     PROMPT_FILE_NAME, 
     OPENAI_MODEL,
     RESPONSE_FORMAT,
+    IDENTITY_HEADER,
     chatRouter,
     openai,
 }
diff --git a/src/chat/post-new-message.ts b/src/chat/post-new-message.ts
index 027e314..0d3a061 100644
--- a/src/chat/post-new-message.ts
+++ b/src/chat/post-new-message.ts
@@ -1,19 +1,17 @@
 import { z } from "zod";
 import { makePostEndpoint } from "../middleware/validation/makePostEndpoint.js";
-import { OPENAI_MODEL, RESPONSE_FORMAT, openai } from "./index.js";
-import { ChatCompletionMessageParam } from "openai/resources/index.js";
+import { IDENTITY_HEADER, OPENAI_MODEL, RESPONSE_FORMAT, openai } from "./index.js";
+import {ChatCompletionMessageParam } from "openai/resources/index.js";
+import { addMessage, getMessages, getUserVisibleMessages } from "../util/messageStore.js";
 
 const ChatCompletionRole = z.union([z.literal('user'), z.literal('system'), z.literal('assistant')]);
 export type ChatCompletionRole = z.infer<typeof ChatCompletionRole>;
 
-const MessageHistory = z.object({
-    messages: z.array(
+const MessageHistory = 
         z.object({
             role: ChatCompletionRole,
             content: z.string(),
-        })
-    ).nonempty()
-});
+        });
 type MessageHistory = z.infer<typeof MessageHistory>;
 
 const makeApiRequest = async (messages: ChatCompletionMessageParam[]) => {
@@ -24,17 +22,26 @@ const makeApiRequest = async (messages: ChatCompletionMessageParam[]) => {
     });
 }
 
-const processMessages = async (messages: ChatCompletionMessageParam[], response: any) => {
+const processMessages = async (messages: ChatCompletionMessageParam[], response: any, identity: string) => {
     const completion = await makeApiRequest(messages);
     const chatResponse = completion.choices[0];
     console.log(chatResponse);
     if(!chatResponse){
         return response.status(500).send("Got no response from the bot");
     }
-    return response.status(200).send(chatResponse.message);
+    addMessage(identity, chatResponse.message);
+    return response.status(200).send(getUserVisibleMessages(identity));
+
 }
 
+
 export const newMessage = makePostEndpoint(MessageHistory, async (request, response) => {
-    const messages = request.body.messages;
-    processMessages(messages, response);
+    const message = request.body;
+    const identity = request.header(IDENTITY_HEADER);
+    if (!identity) {
+        return response.status(400).send(`Missing ${IDENTITY_HEADER} header.`)
+    }
+    addMessage(identity, message);
+    const messages = getMessages(identity) ?? []; //TODO handle no messages
+    return processMessages(messages, response, identity);
 });
diff --git a/src/util/messageStore.ts b/src/util/messageStore.ts
new file mode 100644
index 0000000..39fd233
--- /dev/null
+++ b/src/util/messageStore.ts
@@ -0,0 +1,22 @@
+import { ChatCompletionMessageParam } from "openai/resources";
+import TTLCache from '@isaacs/ttlcache';
+
+const sessionStore = new TTLCache<string, ChatCompletionMessageParam[]>({ max: 10000, ttl: 50 * 60 * 1000 });
+
+export const addMessage = (key: string, message: ChatCompletionMessageParam) => {
+    const value = sessionStore.get(key) ?? [];
+    sessionStore.set(key, [...value, message]);
+}
+
+export const addMessages = (key: string, messages: ChatCompletionMessageParam[]) => {
+    const value = sessionStore.get(key) ?? [];
+    sessionStore.set(key, value.concat(messages));
+}
+
+export const getMessages = (key: string) => {
+    return sessionStore.get(key);
+}
+
+export const getUserVisibleMessages = (key: string) => {
+    return getMessages(key)?.filter(message => message.role === 'user' || message.role === 'assistant' && !message.tool_calls);
+}
\ No newline at end of file