“Peer-to-Peer” (P2P) is a cooperative distribution system which uses distributed resources to perform critical functions in a decentralized manner. This paper reviews the economic literature and studies a qualitative database on P2P experiences. While the economic literature has focused so far on the issue of cooperation among peers and free riding, this article examines three major economic issues of P2P. P2P systems allow the massive pooling of resources and information at a cost and on a scale that would be difficult to achieve in a traditional client-server system. This is the first economic challenge: is the P2P system a mere substitute for client-server systems, or instead, does it create new economic activities made possible by this technology? The second economic issue of P2P is to understand peer cooperation and the stability of this cooperation. The third issue lies in the sustainability of its business model: is P2P just a new technology, a new sharing system, or a new business model? This paper constructs a typology for P2P experiences based on economic characteristics (rivalry, excludability, externalities) and technical characteristics (degree of decentralization).