diff --git a/combo/data/token_indexers/pretrained_transformer_fixed_mismatched_indexer.py b/combo/data/token_indexers/pretrained_transformer_fixed_mismatched_indexer.py
index 493f7f4e18c996ab9c2c7f4f08683055cc431e4a..4a27336d1788bf8b2e829ac081e0295cc5936c32 100644
--- a/combo/data/token_indexers/pretrained_transformer_fixed_mismatched_indexer.py
+++ b/combo/data/token_indexers/pretrained_transformer_fixed_mismatched_indexer.py
@@ -1,3 +1,8 @@
+"""
+Adapted from COMBO
+Authors: Mateusz Klimaszewski, Lukasz Pszenny
+"""
+
 from typing import Optional, Dict, Any, List, Tuple
 
 from overrides import overrides
diff --git a/combo/data/token_indexers/pretrained_transformer_indexer.py b/combo/data/token_indexers/pretrained_transformer_indexer.py
index e00a9c280bb86c8c8502c36a7ea2528acf26d7b4..c81596e9048ec7553a7dde02a6e8bdf19fa5aa97 100644
--- a/combo/data/token_indexers/pretrained_transformer_indexer.py
+++ b/combo/data/token_indexers/pretrained_transformer_indexer.py
@@ -1,3 +1,8 @@
+"""
+Adapted from AllenNLP
+https://github.com/allenai/allennlp/blob/main/allennlp/data/token_indexers/pretrained_transformer_indexer.py
+"""
+
 from typing import Dict, List, Optional, Tuple, Any
 import logging
 import torch
diff --git a/combo/data/token_indexers/pretrained_transformer_mismatched_indexer.py b/combo/data/token_indexers/pretrained_transformer_mismatched_indexer.py
index 6c88343aabe9735c393bd3df3bdd10ed9ebe9c58..20411dddce7096e84753cfb73a42a8d26f584fc0 100644
--- a/combo/data/token_indexers/pretrained_transformer_mismatched_indexer.py
+++ b/combo/data/token_indexers/pretrained_transformer_mismatched_indexer.py
@@ -1,3 +1,8 @@
+"""
+Adapted from AllenNLP
+https://github.com/allenai/allennlp/blob/main/allennlp/data/token_indexers/pretrained_transformer_mismatched_indexer.py
+"""
+
 from typing import Dict, List, Any, Optional
 import logging
 
diff --git a/combo/data/token_indexers/token_const_padding_characters_indexer.py b/combo/data/token_indexers/token_const_padding_characters_indexer.py
index db5e9b7ecba60cd201c664690997733feeb110de..6b7440d79db3cacc84ae4cc5ca54915778880756 100644
--- a/combo/data/token_indexers/token_const_padding_characters_indexer.py
+++ b/combo/data/token_indexers/token_const_padding_characters_indexer.py
@@ -1,4 +1,8 @@
-"""Custom character token indexer."""
+"""
+Custom character token indexer.
+Adapted from COMBO.
+Author: Mateusz Klimaszewski
+"""
 import itertools
 from typing import List, Dict
 
diff --git a/combo/data/token_indexers/token_features_indexer.py b/combo/data/token_indexers/token_features_indexer.py
index 48359412bb5f0db20cf24e46c9ed359623903350..9ae65472862ef21a49063abafa347efd8bbe702e 100644
--- a/combo/data/token_indexers/token_features_indexer.py
+++ b/combo/data/token_indexers/token_features_indexer.py
@@ -1,4 +1,7 @@
-"""Features indexer."""
+"""Features indexer.
+Adapted from COMBO.
+Author: Mateusz Klimaszewski
+"""
 import collections
 from abc import ABC
 from typing import List, Dict