The4th InternationalWorkshoponPeer-to-PeerSystemswasheld atCornellon February 24th and 25th 2005.The IPTPS workshopcontinued to bring together researchersand practitioners from a variety of disciplines, including
networking, theory,databases,security,andscienti?ccomputing. Theydescribedexperim- tal ?ndings, discussed challenges, and presented novel techniques. We received 123 submissions. Submissions were limited to 6 pages, one page
morethanin previousyears.ThesubmissionswerereviewedbyaProgramC- mitteeconsistingof18internationalexpertsfromacademiaandindustry.Aftera bidding process,each committee member was assigned 20 papers to review, g- erating 3
reviews for each paper. Controversial papers were assigned additional reviewers.Thepaperswerethenrankedbasedonoriginality,technicalmerit,and topical relevance,aswell asthe likelihood that the ideas expressedwouldlead to
insightful technical discussions at the workshop. The program chairs suggested a program which was extensively discussed and revised by the entire committee to produce the ?nal program. We accepted 24 papers, which were
organized into 8 sessions: Security and Incentives, Search, Multicast, Overlay Algorithms, Empirical Studies, and N- work Locality, and two sessions on miscellaneous topics. Authors revised their submissions for a
preproceedings distributed at the workshop. After the wo- shop, the authors revised their papers once more for the proceedings before you.