diff --git a/SUMMARY.md b/SUMMARY.md
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+++ b/SUMMARY.md
@@ -5,4 +5,6 @@
   * [API First](core-principles/api-first.md)
   * [OpenAPI Specification](core-principles/openapi-specification.md)
   * [Apiary](core-principles/apiary.md)
+  * [Version Control System](core-principles/version-control-system.md)
+  * [Contract](core-principles/contract.md)
 
diff --git a/core-principles/contract.md b/core-principles/contract.md
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@@ -0,0 +1,4 @@
+# Contract 
+Approved API Design, represented by its API Description, MUST represent the **contract** between API stakeholder, implementers and consumers.
+
+Any change to an API MUST be accompanied by a relevant change in the contract (API Description). 
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diff --git a/core-principles/version-control-system.md b/core-principles/version-control-system.md
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+# Version Control System
+Every API description SHOULD be stored in an Version Control System (Bitbucket, GitHub). Where possible the API description SHOULD stored in the **same** repository as the API implementation.
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