The first chapter gives a brief history of the open source community and the second chapter takes a close look at the relationship between intellectual property rights and software, both open source and proprietary. The next three chapters consider the who, the open source community, the how, software development both within and outside the community, and the what, open source projects and product quality. Chapters 6 and 7 focus on the different users of open source software: companies and governments respectively. These are followed by two chapters that interpret the phenomenon, first from an organizational point of view in Chapter 8 and then using the theory of complex adaptive systems in Chapter 9. The last chapter explores the current and potential applications of the concept underlying open source software in other fields.