In recent years, peer-to-peer file sharing applications have witnessed explosive growth. With millions of simultaneous users and, at some universities, generating three times as much traffic as the Web, this is an important component of the Internet. For my Area Exam, I survey three related topics: Peer-to-Peer Search, Peer-to-Peer File Transfer, and Peer-to-Peer Streaming, examining measurement studies of existing systems and surveying design improvements suggested in the research literature.