By tailoring content access, presentation, and functionality to the user’s location, device, personal preferences and needs, Web Information Systems have become increasingly user- and context dependent. In order to realize such adaptive behavior, Web engineers are thus faced with an additional challenge: engineering the required adaptation concerns. In this article, we present, in the context of a Web Information System design method, an adaptation engineering process that is separated from the regular Web design process. Our approach is based on the use of two key elements: (i) aspect-oriented techniques to achieve the separation of (adaptation) concerns, and (ii) the exploitation of semantic information and meta-data associated with the content, for enhanced expressivity and flexibility. By combining these key elements, we demonstrate a robust, rich, consistent and flexible way to specify adaptation in Web Information Systems.