Intellectual property is an old concept, with the first recorded instances of patents (1449) and copyrights (1662) both occurring in England (“Intellectual property”, Wikipedia, 2004). The first piece of software was submitted for copyright to the United States Copyright Office in 1961, and was accepted as copyrightable under existing copyright law (Hollaar, 2002). The open source movement has relied upon controversial intellectual property rights that are rooted in the overall history of software development (Lerner & Tirole, 2002; von Hippel & von Krogh, 2003). By defining specific legal mechanisms and designing various software licenses, the open source phenomenon has successfully proposed an alternative software development model whose approach to the concept of intellectual property is quite different from that taken by traditional proprietary software. A separate article in this encyclopedia treats open source software communities in general as a type of virtual community. This article takes a historical approach to examining how the intellectual property rights that have protected free/open source software have contributed towards the formation and evolution of virtual communities whose central focus is software projects based on the open source model.