This book contstitutes the refereed proceedings of the European Conference on Web Services, ECOWS 2004, held in Erfurt, Germany, in September 2004. The 21 revised full papers presented were carefully reviewed and selected from numerous submissions. The papers are organised in topical sections on Web service modeling and process management, Web service security and knowledge management, Web service discovery, Web service infrastructure, Web service composition and negotiation, Web service solutions, and semantics in Web services