This book constitutes the refereed proceedings of the 5th IFIP TC6 International Symposium INTERWORKING 2000 on Next Generation Networks held in Bergen, Norway in October 2000. The 33 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers are organized in topical sections on strategic views on future network architecture and services, Internet everywhere and on every network, preparing for the information society with performing networks, European perspective of next generation networks, quality of service and resource management, traffic management and control, bandwidth broker and IP networks, and selective topics in networks.