This book constitutes the refereed proceedings of the Third European Conference on Universal Multiservice Networks, ECUMN 2004, held in Porto, Portugal in October 2004.The 53 revised full papers presented were carefully reviewed and selected from 131 submissions. The papers are organized in topical sections on wireless networks, Quality of Service, QoS, optical networks, mobility management, transport protocols, mobile ad-hoc networks, real-time and multimedia, traffic management, Internet technologies and applications, overlay and virtual private networks, network security and privacy, network operations and management, and wireless and sensor networks.