This chapter reviews core concepts of peer-to-peer (P2P) networking. It highlights the management of resources, such as bandwidth, storage, information, files, and processor cycles based on P2P networks. A model differentiating P2P infrastructures, P2P applications, and P2P communities is introduced. This model provides a better understanding of the different perspectives of P2P. Key technical and social challenges that still limit the potential of information systems based on P2P architectures are discussed.