Adaptive Educational Hypermedia systems (AEH) enhance learning by adaptation and personalisation. As a consequence, wide ranging knowledge and learning content are needed. Problems then emerge in the provision of suitable authoring tools to carry out the authoring process which is complex and time consuming. Based on the fact that former research studies on authoring have identified drawbacks in collaboration, usabilility, efficiency, or interoperability, this paper proposes an approach for collaborative adaptation authoring for adaptive learning. The intended approach aims at improving authoring for AEH systems by allowing many people to participate and enhancing authors' interaction. The novelty of the approach lies in how the domain knowledge which has been semantically defined is enriched, and in the application of Computer Support Collaborative Work (CSCW). This approach adopts the advantages of existing semantic web technology and wiki-based authoring tools used to develop domain knowledge; its output is then enriched with pedagogy-related knowledge including adaptation. The output of the system is intended to be delivered in an existing AEH system.