diff --git a/podium/datasets/dataset_abc.py b/podium/datasets/dataset_abc.py
index 3f40f6ef..56eaa4a8 100644
--- a/podium/datasets/dataset_abc.py
+++ b/podium/datasets/dataset_abc.py
@@ -117,7 +117,7 @@ def finalize_fields(self, *datasets: "DatasetABC") -> None:
                 for example in dataset:
                     for field in fields_to_build:
                         _, tokenized = example[field.name]
-                        field.update_vocab(tokenized)
+                        field.update_numericalizer(tokenized)
 
         for field in self.fields:
             field.finalize()
diff --git a/podium/preproc/__init__.py b/podium/preproc/__init__.py
index 66c141af..5bbe654a 100644
--- a/podium/preproc/__init__.py
+++ b/podium/preproc/__init__.py
@@ -9,6 +9,7 @@
     TextCleanUp,
 )
 from .lemmatizer import CroatianLemmatizer
+from .numericalizer_abc import NumericalizerABC
 from .sentencizers import SpacySentencizer
 from .stemmer import CroatianStemmer
 from .tokenizers import get_tokenizer
diff --git a/podium/preproc/numericalizer_abc.py b/podium/preproc/numericalizer_abc.py
new file mode 100644
index 00000000..b24e3f3a
--- /dev/null
+++ b/podium/preproc/numericalizer_abc.py
@@ -0,0 +1,93 @@
+from abc import ABC, abstractmethod
+from typing import List
+
+import numpy as np
+
+
+class NumericalizerABC(ABC):
+    """ABC that contains the interface for Podium numericalizers. Numericalizers are used
+    to transform tokens into vectors or any other custom datatype during batching.
+
+    Attributes
+    ----------
+    finalized: bool
+        Whether this numericalizer was finalized and is able to be used for
+        numericalization.
+    """
+
+    def __init__(self, eager=True):
+        """Initialises the Numericalizer.
+
+        Parameters
+        ----------
+        eager: bool
+            Whether the Numericalizer is to be updated during loading of the dataset, or
+            after all data is loaded.
+
+        """
+        self._finalized = False
+        self._eager = eager
+
+    @abstractmethod
+    def numericalize(self, tokens: List[str]) -> np.ndarray:
+        """Converts `tokens` into a numericalized format used in batches.
+        Numericalizations are most often numpy vectors, but any custom datatype is
+        supported.
+
+        Parameters
+        ----------
+        tokens: List[str]
+            A list of strings that represent the tokens of this data point. Can also be
+            any other datatype, as long as this Numericalizer supports it.
+
+        Returns
+        -------
+        Numericalization used in batches. Numericalizations are most often numpy vectors,
+        but any custom datatype is supported.
+        """
+        pass
+
+    def finalize(self):
+        """Finalizes the Numericalizer and prepares it for numericalization.
+        This method must be overridden in classes that require finalization before
+        numericalization. The override must call `mark_finalize` after successful
+        completion."""
+        self.mark_finalized()
+        pass
+
+    def update(self, tokens: List[str]) -> None:
+        """Updates this Numericalizer with a single data point. Numericalizers that need
+        to be updated example by example must override this method. Numericalizers that
+        are eager get updated during the dataset loading process, while non-eager ones get
+        updated after loading is finished, after all eager numericalizers were fully
+        updated.
+
+        Parameters
+        ----------
+        tokens: List[str]
+            A list of strings that represent the tokens of this data point. Can also be
+            any other datatype, as long as this Numericalizer supports it.
+
+        """
+        pass
+
+    def mark_finalized(self) -> None:
+        """Marks the field as finalized. This method must be called after finalization
+        completes successfully."""
+        self._finalized = True
+
+    @property
+    def finalized(self) -> bool:
+        """Whether this Numericalizer was finalized and is ready for numericalization."""
+        return self._finalized
+
+    @property
+    def eager(self) -> bool:
+        """Whether this Numericalizer is eager. Numericalizers that
+        are eager get updated during the dataset loading process, while non-eager ones get
+        updated after loading is finished, after all eager numericalizers were fully
+        updated."""
+        return self._eager
+
+    def __call__(self, tokens: List[str]) -> np.ndarray:
+        return self.numericalize(tokens)
diff --git a/podium/storage/field.py b/podium/storage/field.py
index d1595b27..a4cc1429 100644
--- a/podium/storage/field.py
+++ b/podium/storage/field.py
@@ -6,6 +6,7 @@
 
 import numpy as np
 
+from podium.preproc import NumericalizerABC
 from podium.preproc.tokenizers import get_tokenizer
 from podium.storage.vocab import Vocab
 
@@ -13,7 +14,8 @@
 PretokenizationHookType = Callable[[Any], Any]
 PosttokenizationHookType = Callable[[Any, List[str]], Tuple[Any, List[str]]]
 TokenizerType = Optional[Union[str, Callable[[Any], List[str]]]]
-NumericalizerType = Callable[[str], Union[int, float]]
+NumericalizerCallableType = Callable[[str], Union[int, float]]
+NumericalizerType = Union[NumericalizerABC, NumericalizerCallableType]
 
 
 class PretokenizationPipeline:
@@ -205,6 +207,16 @@ def remove_pretokenize_hooks(self):
         self._pretokenization_pipeline.clear()
 
 
+class NumericalizerCallableWrapper(NumericalizerABC):
+    def __init__(self, numericalizer: NumericalizerType):
+        super().__init__(eager=True)
+        self._wrapped_numericalizer = numericalizer
+
+    def numericalize(self, tokens: List[str]) -> np.ndarray:
+        numericalized = [self._wrapped_numericalizer(tok) for tok in tokens]
+        return np.array(numericalized)
+
+
 class Field:
     """Holds the preprocessing and numericalization logic for a single
     field of a dataset.
@@ -321,12 +333,16 @@ def __init__(
         else:
             self._tokenizer = get_tokenizer(tokenizer)
 
-        if isinstance(numericalizer, Vocab):
-            self._vocab = numericalizer
-            self._numericalizer = self.vocab.__getitem__
-        else:
-            self._vocab = None
+        if isinstance(numericalizer, NumericalizerABC) or numericalizer is None:
             self._numericalizer = numericalizer
+        elif isinstance(numericalizer, Callable):
+            self._numericalizer = NumericalizerCallableWrapper(numericalizer)
+        else:
+            err_msg = (
+                f"Field {name}: unsupported numericalizer type "
+                f'"{type(numericalizer).__name__}"'
+            )
+            raise TypeError(err_msg)
 
         self._keep_raw = keep_raw
 
@@ -385,12 +401,20 @@ def eager(self):
             whether this field has a Vocab and whether that Vocab is
             marked as eager
         """
-        return self.vocab is not None and self.vocab.eager
+        # Pretend to be eager if no numericalizer provided
+        return self._numericalizer is None or self._numericalizer.eager
 
     @property
     def vocab(self):
         """"""
-        return self._vocab
+        if not self.use_vocab:
+            numericalizer_type = type(self._numericalizer).__name__
+            err_msg = (
+                f'Field "{self.name}" has no vocab, numericalizer type is '
+                f"{numericalizer_type}."
+            )
+            raise TypeError(err_msg)
+        return self._numericalizer
 
     @property
     def use_vocab(self):
@@ -402,7 +426,7 @@ def use_vocab(self):
             Whether the field uses a vocab or not.
         """
 
-        return self.vocab is not None
+        return isinstance(self._numericalizer, Vocab)
 
     @property
     def is_target(self):
@@ -547,6 +571,7 @@ def preprocess(
 
         # Preprocess the raw input
         # TODO keep unprocessed or processed raw?
+        # Keeping processed for now, may change in the future
         processed_raw = self._run_pretokenization_hooks(data)
         tokenized = (
             self._tokenizer(processed_raw)
@@ -556,7 +581,7 @@ def preprocess(
 
         return (self._process_tokens(processed_raw, tokenized),)
 
-    def update_vocab(self, tokenized: List[str]):
+    def update_numericalizer(self, tokenized: Union[str, List[str]]) -> None:
         """Updates the vocab with a data point in its tokenized form.
         If the field does not do tokenization,
 
@@ -567,11 +592,11 @@ def update_vocab(self, tokenized: List[str]):
             updated with.
         """
 
-        if not self.use_vocab:
+        if self._numericalizer is None:
             return  # TODO throw Error?
 
         data = tokenized if isinstance(tokenized, (list, tuple)) else (tokenized,)
-        self._vocab += data
+        self._numericalizer.update(data)
 
     @property
     def finalized(self) -> bool:
@@ -584,13 +609,13 @@ def finalized(self) -> bool:
             Whether the field's Vocab vas finalized. If the field has no
             vocab, returns True.
         """
-        return True if self.vocab is None else self.vocab.finalized
+        return self._numericalizer is None or self._numericalizer.finalized
 
     def finalize(self):
         """Signals that this field's vocab can be built."""
 
-        if self.use_vocab:
-            self.vocab.finalize()
+        if self._numericalizer is not None:
+            self._numericalizer.finalize()
 
     def _process_tokens(
         self, raw: Any, tokens: Union[Any, List[str]]
@@ -616,8 +641,12 @@ def _process_tokens(
         raw, tokenized = self._run_posttokenization_hooks(raw, tokens)
         raw = raw if self._keep_raw else None
 
-        if self.eager and not self.vocab.finalized:
-            self.update_vocab(tokenized)
+        if (
+            self.eager
+            and self._numericalizer is not None
+            and not self._numericalizer.finalized
+        ):
+            self.update_numericalizer(tokenized)
         return self.name, (raw, tokenized)
 
     def get_default_value(self) -> Union[int, float]:
@@ -679,10 +708,7 @@ def numericalize(
 
         tokens = tokenized if isinstance(tokenized, (list, tuple)) else [tokenized]
 
-        if self.use_vocab:
-            return self.vocab.numericalize(tokens)
-        else:
-            return np.array([self._numericalizer(t) for t in tokens])
+        return self._numericalizer.numericalize(tokens)
 
     def _pad_to_length(
         self,
@@ -1030,9 +1056,8 @@ def __init__(
 
     def finalize(self):
         """Signals that this field's vocab can be built."""
-        super().finalize()
         if self._num_of_classes is None:
-            self.fixed_length = self._num_of_classes = len(self.vocab)
+            self._fixed_length = self._num_of_classes = len(self.vocab)
 
         if self.use_vocab and len(self.vocab) > self._num_of_classes:
             raise ValueError(
@@ -1040,6 +1065,7 @@ def finalize(self):
                 f"of classes. Declared: {self._num_of_classes}, "
                 f"Actual: {len(self.vocab)}"
             )
+        super().finalize()
 
     def numericalize(
         self, data: Tuple[Optional[Any], Optional[Union[Any, List[str]]]]
diff --git a/podium/storage/vectorizers/tfidf.py b/podium/storage/vectorizers/tfidf.py
index 1e6f855f..dab91e9c 100644
--- a/podium/storage/vectorizers/tfidf.py
+++ b/podium/storage/vectorizers/tfidf.py
@@ -149,7 +149,7 @@ def fit(self, dataset, field):
         ValueError
             If the vocab or fields vocab are None
         """
-        if self._vocab is None and (field is None or field.vocab is None):
+        if self._vocab is None and (field is None or not field.use_vocab):
             raise ValueError(
                 "Vocab is not defined. User should define vocab in constructor "
                 "or by providing field with a non-empty vocab property."
diff --git a/podium/storage/vocab.py b/podium/storage/vocab.py
index c8ed1b34..76eb458e 100644
--- a/podium/storage/vocab.py
+++ b/podium/storage/vocab.py
@@ -3,10 +3,12 @@
 from collections import Counter
 from enum import Enum
 from itertools import chain
-from typing import Iterable, Union
+from typing import Iterable, List, Union
 
 import numpy as np
 
+from podium.preproc import NumericalizerABC
+
 
 def unique(values: Iterable):
     """Generator that iterates over the first occurrence of every value in values,
@@ -60,7 +62,7 @@ class SpecialVocabSymbols(Enum):
     PAD = "<pad>"
 
 
-class Vocab:
+class Vocab(NumericalizerABC):
     """Class for storing vocabulary. It supports frequency counting and size
     limiting.
 
@@ -97,6 +99,7 @@ def __init__(
             if true word frequencies will be saved for later use on
             the finalization
         """
+        super(Vocab, self).__init__(eager)
         self._freqs = Counter()
         self._keep_freqs = keep_freqs
         self._min_freq = min_freq
@@ -112,8 +115,6 @@ def __init__(
         self.stoi.update({k: v for v, k in enumerate(self.itos)})
 
         self._max_size = max_size
-        self.eager = eager
-        self.finalized = False  # flag to know if we're ready to numericalize
 
     @staticmethod
     def _init_default_unk_index(specials):
@@ -194,6 +195,9 @@ def padding_index(self):
             raise ValueError("Padding symbol is not in the vocabulary.")
         return self.stoi[SpecialVocabSymbols.PAD]
 
+    def update(self, tokens: List[str]) -> None:
+        self.__iadd__(tokens)
+
     def __iadd__(self, values: Union["Vocab", Iterable]):
         """Adds additional values or another Vocab to this Vocab.
 
@@ -375,7 +379,7 @@ def finalize(self):
 
         if not self._keep_freqs:
             self._freqs = None  # release memory
-        self.finalized = True
+        self.mark_finalized()
 
     def numericalize(self, data):
         """Method numericalizes given tokens.
diff --git a/tests/arrow/test_pyarrow_tabular_dataset.py b/tests/arrow/test_pyarrow_tabular_dataset.py
index 8acf5249..0d62c7af 100644
--- a/tests/arrow/test_pyarrow_tabular_dataset.py
+++ b/tests/arrow/test_pyarrow_tabular_dataset.py
@@ -139,21 +139,23 @@ def test_dump_and_load(pyarrow_dataset):
 def test_finalize_fields(data, fields, mocker):
     for field in fields:
         mocker.spy(field, "finalize")
-        mocker.spy(field, "update_vocab")
+        mocker.spy(field, "update_numericalizer")
 
     dataset = pyarrow_dataset(data, fields)
 
     for f in fields:
         # before finalization, no field's dict was updated
-        if f.vocab is not None:
-            assert not f.finalized
+        if f._numericalizer is not None:
+            assert not f._numericalizer.finalized
 
     dataset.finalize_fields()
 
-    fields_to_finalize = [f for f in fields if not f.eager and f.use_vocab]
+    fields_to_finalize = [
+        f for f in fields if not f.eager and f._numericalizer is not None
+    ]
     for f in fields_to_finalize:
         # during finalization, only non-eager field's dict should be updated
-        assert f.update_vocab.call_count == (len(data) if (not f.eager) else 0)
+        assert f.update_numericalizer.call_count == (len(data) if (not f.eager) else 0)
         f.finalize.assert_called_once()
         # all fields should be finalized
         assert f.finalized
diff --git a/tests/storage/test_dataset.py b/tests/storage/test_dataset.py
index ef55a0f7..5e453071 100644
--- a/tests/storage/test_dataset.py
+++ b/tests/storage/test_dataset.py
@@ -78,7 +78,7 @@ def preprocess(self, data):
 
         return ((self.name, (raw, tokenized)),)
 
-    def update_vocab(self, tokenized):
+    def update_numericalizer(self, tokenized):
         assert not self.eager
         self.updated_count += 1
 
diff --git a/tests/storage/test_field.py b/tests/storage/test_field.py
index 6f785512..1979602e 100644
--- a/tests/storage/test_field.py
+++ b/tests/storage/test_field.py
@@ -5,6 +5,7 @@
 import numpy as np
 import pytest
 
+from podium.preproc import NumericalizerABC
 from podium.storage import (
     Field,
     LabelField,
@@ -36,17 +37,19 @@ def tokenizer(self, string):
         return MockTokenizer()
 
 
-class MockVocab(Mock):
+class MockVocab(Mock, NumericalizerABC):
     def __init__(self, eager=True):
-        super(MockVocab, self).__init__(spec=Vocab)
+        Mock.__init__(self, spec=Vocab)
+        NumericalizerABC.__init__(self, eager)
         self.values = []
-        self.finalized = False
         self.numericalized = False
-        self.eager = eager
 
     def padding_index(self):
         return PAD_NUM
 
+    def update(self, tokens):
+        self.__iadd__(tokens)
+
     def __add__(self, values):
         if type(values) == type(self):
             pass
@@ -61,8 +64,7 @@ def __iadd__(self, other):
     def finalize(self):
         if self.finalized:
             raise Exception
-        else:
-            self.finalized = True
+        self.mark_finalized()
 
     def numericalize(self, data):
         self.numericalized = True