Peer-to-peer (p2p), initially conceived for the purpose of sharing music in the Internet, is emerging as a much more general paradigm for the construction of resilient, large-scale, distributed services and applications. We define p2p systems broadly as self-organizing, decentralized distributed systems in which nodes play symmetric roles. The scalability and resilience of such systems lends itself to a growing domain of applications beyond file sharing. At the same time, the scale, decentralization, diversity and potentially open membership in these systems pose difficult problems, particularly in resource management and security.

Recent work on structured overlay networks (sometimes called "distributed hash tables") has made significant strides towards simplifying the construction of robust, large-scale distributed applications. These overlays effectively shield application designers from the complexities of organizing and maintaining an overlay network, tolerating node failures, balancing load and locating application objects.

In this talk, I'll sketch the state-of-the-art in structured overlays that provide self-organization, fault-tolerance, efficient object location and proximity-aware overlay construction. We'll consider potential applications, including cooperative network storage, ad hoc collaboration, scalable event notification and bulk content distribution. I'll conclude with an outlook on key research problems and future directions.