diff --git a/CHANGELOG.md b/CHANGELOG.md
index cc629c1..9f7d9ee 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,16 +17,12 @@ This project follows **Semantic Versioning (SemVer)** ([semver.org](https://semv
 
 ---
 
-## [Unreleased] 
+## [0.90.0] 2026-08-25
 
-### Added 
-- Placeholder for upcoming features and enhancements. 
+### Initial Features
 
-### Fixed 
-- Placeholder for bug fixes and security updates. 
-
-### Changed 
-- Placeholder for changes to existing functionality. 
+- Key functionality (in Python) for providing useful helper classes to build and create security labels.
+- Added SPDX headers.
 
 ---
 
diff --git a/ianode_labels/__init__.py b/ianode_labels/__init__.py
index d10581e..3d34d0a 100644
--- a/ianode_labels/__init__.py
+++ b/ianode_labels/__init__.py
@@ -1,25 +1,32 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
+
+
 from ianode_labels.idh_model import IDHModel
 from ianode_labels.security_labels import Label, MultiValueLabel, SecurityLabelBuilder, SingleValueLabel
 from ianode_labels.ianode_model import IANodeModel
 from ianode_labels.ianodev1 import IANodeLabelsV1
 from ianode_labels.ianodev2 import IANodeSecurityLabelsV2
 
-__license__ = """
-Copyright (c) Telicent Ltd.
-
-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.
-"""
-
 
 __all__ = [
     "SecurityLabelBuilder",
diff --git a/ianode_labels/ianode_model.py b/ianode_labels/ianode_model.py
index 64eadd4..b528e5e 100644
--- a/ianode_labels/ianode_model.py
+++ b/ianode_labels/ianode_model.py
@@ -1,3 +1,26 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
+
+
 import logging
 from abc import ABC, abstractmethod
 from datetime import datetime, timezone
@@ -8,21 +31,6 @@
 from ianode_labels.security_labels import SecurityLabelBuilder
 from ianode_labels.ianodev2 import IANodeSecurityLabelsV2
 
-__license__ = """
-Copyright (c) Telicent Ltd.
-
-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.
-"""
 
 log = logging.getLogger(__name__)
 
diff --git a/ianode_labels/ianodev1.py b/ianode_labels/ianodev1.py
index c2d3a87..7f86802 100644
--- a/ianode_labels/ianodev1.py
+++ b/ianode_labels/ianodev1.py
@@ -1,22 +1,29 @@
-from enum import Enum
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
 
-from ianode_labels import security_labels as security
 
-__license__ = """
-Copyright (c) Telicent Ltd.
+# Copyright (c) Telicent Ltd.
+#
+# 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.
 
-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
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
 
-    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 enum import Enum
+
+from ianode_labels import security_labels as security
 
 
 class IANodeLabelsV1(Enum):
diff --git a/ianode_labels/ianodev2.py b/ianode_labels/ianodev2.py
index b9acd9f..1ffcde7 100644
--- a/ianode_labels/ianodev2.py
+++ b/ianode_labels/ianodev2.py
@@ -1,22 +1,30 @@
-from enum import Enum
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
 
-from ianode_labels.security_labels import MultiValueLabel, SingleValueLabel
 
-__license__ = """
-Copyright (c) Telicent Ltd.
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
 
-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
+from enum import Enum
+
+from ianode_labels.security_labels import MultiValueLabel, SingleValueLabel
 
-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.
-"""
 
 
 class AndGroups(MultiValueLabel):
diff --git a/ianode_labels/idh_model.py b/ianode_labels/idh_model.py
index 27ad6e1..50a3b64 100644
--- a/ianode_labels/idh_model.py
+++ b/ianode_labels/idh_model.py
@@ -1,3 +1,26 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
+
+
 import logging
 from datetime import datetime, timezone
 from typing import Annotated
@@ -7,21 +30,6 @@
 from ianode_labels.security_labels import SecurityLabelBuilder
 from ianode_labels.ianodev2 import IANodeSecurityLabelsV2
 
-__license__ = """
-Copyright (c) Telicent Ltd.
-
-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.
-"""
 
 log = logging.getLogger(__name__)
 
diff --git a/ianode_labels/security_labels.py b/ianode_labels/security_labels.py
index 4af3e10..cb49c7e 100644
--- a/ianode_labels/security_labels.py
+++ b/ianode_labels/security_labels.py
@@ -1,18 +1,24 @@
-__license__ = """
-Copyright (c) Telicent Ltd.
-
-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.
-"""
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
 
 
 class Label:
diff --git a/test/__init__.py b/test/__init__.py
index e69de29..a8a7ebe 100644
--- a/test/__init__.py
+++ b/test/__init__.py
@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
\ No newline at end of file
diff --git a/test/test_idh_model.py b/test/test_idh_model.py
index 66efb86..88bed6e 100644
--- a/test/test_idh_model.py
+++ b/test/test_idh_model.py
@@ -1,3 +1,26 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
+
+
 import unittest
 
 from ianode_labels import IDHModel
diff --git a/test/test_security_labels.py b/test/test_security_labels.py
index 944b110..3a6aa9d 100644
--- a/test/test_security_labels.py
+++ b/test/test_security_labels.py
@@ -1,3 +1,26 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
+
+
 import unittest
 
 from ianode_labels import SecurityLabelBuilder, IANodeSecurityLabelsV2
diff --git a/test/test_security_labels_ianode_model.py b/test/test_security_labels_ianode_model.py
index cfa506e..6269e5e 100644
--- a/test/test_security_labels_ianode_model.py
+++ b/test/test_security_labels_ianode_model.py
@@ -1,3 +1,26 @@
+# SPDX-License-Identifier: Apache-2.0
+# Originally developed by Telicent Ltd.; subsequently adapted, enhanced, and maintained by the National Digital Twin Programme.
+
+
+# Copyright (c) Telicent Ltd.
+#
+# 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.
+
+# Modifications made by the National Digital Twin Programme (NDTP)
+# © Crown Copyright 2026. This work has been developed by the National Digital Twin Programme
+# and is legally attributed to the UK's Department for Business, Innovation, Science and Trade (BIST) as the governing entity.
+
+
 import unittest
 
 from ianode_labels import SecurityLabelBuilder, IANodeLabelsV1