A peer-to-peer (or P2P) computer network is a network that relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers. P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes. Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as telephony traffic, is also passed using P2P technology.

A pure peer-to-peer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network. This model of network arrangement differs from the client-server model where communication is usually to and from a central server. A typical example for a non peer-to-peer file transfer is an FTP server where the client and server programs are quite distinct, and the clients initiate the download/uploads and the servers react to and satisfy these requests.

• Pure P2P Network: un sistema totalmente decentralizzato (cfr. Rete paritetica), non c'è un server centrale ma solo nodi. Quando un utente entra in rete si collega ad uno qualsiasi dei nodi (chiamato Entry-Point) offrendo servizi in broadcasting.
• P2P Network with a simple discovery server: quando un utente entra nel network si collega al server principale, che offre servizi di directory (lista degli utenti).
• P2P with a Discovery, Lookup, and Content Server: quando un utente entra nel network si collega al server principale, che offre servizi di directory avanzate (lista degli utenti e delle risorse, lookup).