On behalf of the Organizing and Program Committees of the 3rd European Conference on Universal Multiservice Networks (ECUMN 2004), it is our great pleasure to introduce the proceedings of ECUMN 2004, which was held during October 25–27, 2004, in Porto, Portugal. In response to the Call for Papers, a total of 131 papers were submitted from 29 countries. Each paper was reviewed by several members of the Technical Program Committee or by external peer reviewers. After careful assessment of the reviews, 53 papers were accepted for presentation in 13 technical sessions; half of them originated from countries outside Europe (mainly Asia). This illustrates the strong interest of this conference beyond its original geographical area. The conference program covered a variety of leading-edge research topics which are of current interest, such as wireless networks, mobile ad hoc networks, sensor networks, mobility management, optical networks, quality of service and traffic, transport prools, real-time and multimedia, Internet technologies and applications, overlay and virtual private networks, security and privacy, and network operations and management. Together with three plenary sessions from France T´ el´ ecom, Siemens, and Cisco Systems, these technical presentations - dressed the latest research results from the international industry and academia and reported on findings on present and future multiservice networks.