In very short time, peer-to-peer computing has evolved from an attractive new paradigm into an exciting and vibrant research field bringing together researchers from systems, networking, and theory. This book constitutes the thoroughly refereed post-proceedings of the Second International Workshop on Peer-to-Peer Systems, IPTPS 2003, held in Berkeley, CA, USA in February 2003. The 27 revised papers presented together with an introductory summary of the discussions at the workshop were carefully selected during two rounds of reviewing and revision from initially 166 submissions. The papers are organized in topical sections on experience with P2P; theory and algorithms, P2P in a broader perspective; incentive and fairness; new DHT designs; naming, indexing, and searching; file sharing; and networking and applications.