Peer-to-peer(P2P)computingiscurrentlyattractingenormousmediaattention, spurred by the popularity of ?le sharing systems such as Napster, Gnutella and Morpheus. In P2P systems a very large number of autonomous computing nodes (the peers) pool together their resources and rely on each other for data and services. The wealth of business opportunities promised by P2P networks has gene- ted much industrial interest recently, and has resulted in the creation of various industrial projects, startup companies, and special interest groups. Researchers from distributed computing, networks, agents and databases have also become excited about the P2P vision, and papers tackling open problems in this area have started appearing in high-quality conferences and workshops. Much