This book constitutes the refereed proceedings of the 5th International Conference on Electronic Commerce and Web Technologies, EC-Web 2004, held in Zaragossa, Spain in August/September 2004. The 36 revised full papers presented were carefully reviewed and selected from 103 submissions. The papers are organized in topical sections on recommender systems, databases and EC applications, service-oriented e-commerce applications, electronic negotiation systems, security and trust in e-commerce techniques for b2b e-commerce, negotiation strategies and protocols, modeling of e-commerce applications, e-commerce intelligence, e-retailing and Website design, and digital rights management and EC strategies.