diff --git a/tetrahydra/core.py b/tetrahydra/core.py
index 4879c54..5b8e2a7 100644
--- a/tetrahydra/core.py
+++ b/tetrahydra/core.py
@@ -1,5 +1,21 @@
 """Core functions used in compositional data analysis."""
 
+# Part of Tetrahydra library
+# Copyright (C) 2016-2017  Omer Faruk Gulban
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
 from __future__ import division
 import numpy as np
 from scipy.linalg import helmert
diff --git a/tetrahydra/utils.py b/tetrahydra/utils.py
index 8eef239..af02e64 100644
--- a/tetrahydra/utils.py
+++ b/tetrahydra/utils.py
@@ -1,5 +1,21 @@
 """Utility functions."""
 
+# Part of Tetrahydra library
+# Copyright (C) 2016-2017  Omer Faruk Gulban
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
 from __future__ import division
 import sys
 import numpy as np