diff --git a/calendarweek/calendarweek.py b/calendarweek/calendarweek.py
index 1a0ceed312e3f3d8253220c775e901135cee7d40..264b0c43f3b087e1a37fee37f33fbbbe09ae176c 100644
--- a/calendarweek/calendarweek.py
+++ b/calendarweek/calendarweek.py
@@ -1,3 +1,18 @@
+# Copyright 2019, 2020 Dominik George <dominik.george@teckids.org>
+# Copyright 2020 Jonathan Weth <wethjo@katharineum.de>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 from __future__ import annotations
 
 import calendar
diff --git a/calendarweek/django.py b/calendarweek/django.py
index fe962d5bd89a5adc9a186300eda291a02487c99e..d9d72a0631f92c7aa5cfda446f03d02aec3818d0 100644
--- a/calendarweek/django.py
+++ b/calendarweek/django.py
@@ -1,3 +1,18 @@
+# Copyright 2019, 2020 Dominik George <dominik.george@teckids.org>
+# Copyright 2020 Jonathan Weth <wethjo@katharineum.de>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 import json
 import locale
 from typing import Any, List, Optional, Tuple
diff --git a/calendarweek/util.py b/calendarweek/util.py
index 913c0f494dd50662c99425e8aac76493e131a033..4c7cd7a2c8caec87804f3aca7290f5318423083f 100644
--- a/calendarweek/util.py
+++ b/calendarweek/util.py
@@ -1,3 +1,17 @@
+# Copyright 2019, 2020 Dominik George <dominik.george@teckids.org>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
 from locale import getpreferredencoding, locale_alias, locale_encoding_alias
 from typing import Optional