This book constitutes the refereed proceedings of the Third International Conference on Adaptive Hypermedia and Adaptive Web-Based Systems, AH 2004, held in Eindhoven, The Netherlands in August 2004. The 27 revised full papers and 18 revised short papers presented together with 3 abstracts of keynote talks, 4 doctoral consortium presentations, and 17 posters were carefully reviewed and selected from 138 submissions. The papers provide an excellent view on innovative personalization and adaptation functionalities in a variety of areas including e-learning, e-commerce, mobile tourist guides, etc; they also show the integration of personalization functionalities employed in Web environments, in ambient intelligence and intelligent agents contexts, and building upon adaptive hypermedia and semantic Web technologies, Web search, Web services, social and peer-to-peer networks, and recommender systems.