This book constitutes the refereed proceedings of the 4th International Conference on Adaptive Hypermedia and Adaptive Web-Based Systems, AH 2006, held in Dublin, Ireland in June 2006.The 22 revised full papers and 19 revised short papers presented together with abstracts of 3 keynotes, 12 poster papers, and 14 doctoral consortium posters were carefully reviewed and selected from 122 papers submitted. The papers focus on pioneering theories, techniques, and innovative technologies to provide dynamic personalization, adaptation, and contextualization of hypermedia resources and services.