This special issue of the journal Concurrency and Computation: Practice and Experience is intended to call further attention to Peer-to-Peer (P2P) systems. P2P systems are decentralized, selforganizing distributed systems that cooperate to exchange data. These systems have emerged as the dominant consumer of residential bandwidth, and are being increasingly used in many different application domains. In the last few years, research on P2P systems has been quite intensive, and has produced remarkable results in scalability, robustness, location, distributed storage, censorship resiliency, anonymity, and system measurements. Consequently, P2P systems continue to evolve, differentiating the state of the art from earlier instantiations such as file sharing.
I believe that greater attention to these themes will be broadly enriching for concurrency and computation theory, research and application.
The idea of organizing this special issue developed during the Hot-P2P '06, the third International Workshop on Hot Topics in Peer-to-Peer Systems, sponsored by the IEEE Computer Society and by the Italian FIRB 'WEB-MINDS' project (Wide scalE, Broadband MIddleware for Network Distributed Systems), held in Rhodes, Greece, on 29th April 2006. In this occasion, it was decided to add more visibility to the best papers and their institution. I took the responsibility to select eight papers which were required to provide substantial added contents and to pass further peer review.
Hot-P2P '06 is an international meeting that brings together researchers and practitioners, from both industry and academia, in the fields of systems, networking, and theory. It represents an opportunity to share the latest research results and ideas on P2P systems, thereby promoting research activities in this area. The third edition of the workshop follows the first one, held on 8th October 2004 in Volendam (The Netherlands), and the second one, held on 21st July 2005 in San Diego (California).
I would like to take this opportunity to thank the Editor-in-Chief Professor Geoffrey Fox for his guidance and support. I would also like to express my deepest gratitude to the invited reviewers for their valuable and timely reviews.
Hence, together with the other contributing authors, I offer this special issue of the journal Concurrency and Computation: Practice and Experience devoted to Peer-to-Peer (P2P) systems.