diff --git a/src/GDXFile.jl b/src/GDXFile.jl
index 37fe65f..d787414 100644
--- a/src/GDXFile.jl
+++ b/src/GDXFile.jl
@@ -1,3 +1,9 @@
+# Copyright (c) 2026 Martin Kirk Bonde, James Daniel Foster and contributors
+# Copyright (c) 2020-2023 GAMS Software GmbH
+#
+# Use of this source code is governed by an MIT-style license that can be found
+# in the LICENSE.md file or at https://opensource.org/licenses/MIT.
+
 # High-level GDX file API for GDXInterface.jl
 
 # =============================================================================
diff --git a/src/GDXInterface.jl b/src/GDXInterface.jl
index d083cbf..717d1de 100644
--- a/src/GDXInterface.jl
+++ b/src/GDXInterface.jl
@@ -1,3 +1,9 @@
+# Copyright (c) 2026 Martin Kirk Bonde, James Daniel Foster and contributors
+# Copyright (c) 2020-2023 GAMS Software GmbH
+#
+# Use of this source code is governed by an MIT-style license that can be found
+# in the LICENSE.md file or at https://opensource.org/licenses/MIT.
+
 module GDXInterface
 
 import DataAPI
diff --git a/src/gdx_c_api.jl b/src/gdx_c_api.jl
index 21250ab..62973dc 100644
--- a/src/gdx_c_api.jl
+++ b/src/gdx_c_api.jl
@@ -1,3 +1,9 @@
+# Copyright (c) 2026 Martin Kirk Bonde, James Daniel Foster and contributors
+# Copyright (c) 2020-2023 GAMS Software GmbH
+#
+# Use of this source code is governed by an MIT-style license that can be found
+# in the LICENSE.md file or at https://opensource.org/licenses/MIT.
+
 # GDX library bindings (for libgdx)
 # Low-level C API wrappers for reading and writing GDX files
 
diff --git a/test/runtests.jl b/test/runtests.jl
index 95972a5..0056758 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,3 +1,9 @@
+# Copyright (c) 2026 Martin Kirk Bonde, James Daniel Foster and contributors
+# Copyright (c) 2020-2023 GAMS Software GmbH
+#
+# Use of this source code is governed by an MIT-style license that can be found
+# in the LICENSE.md file or at https://opensource.org/licenses/MIT.
+
 import Test: @testset, @test, @test_throws
 import Tables
 import DataFrames: DataFrame, names, metadata!
diff --git a/test/test_gdxfile.jl b/test/test_gdxfile.jl
index b5f3852..4174740 100644
--- a/test/test_gdxfile.jl
+++ b/test/test_gdxfile.jl
@@ -1,3 +1,9 @@
+# Copyright (c) 2026 Martin Kirk Bonde, James Daniel Foster and contributors
+# Copyright (c) 2020-2023 GAMS Software GmbH
+#
+# Use of this source code is governed by an MIT-style license that can be found
+# in the LICENSE.md file or at https://opensource.org/licenses/MIT.
+
 # Tests for GDXFile API
 
 # For reference: script to create test file "gams_gdx_test.gdx" using GAMS