The open source movement is a group of volunteer programmers that has recently caused quite a stir in the software market. The volunteers of this group develop computer operating systems, programming languages, and other software. They work together in teams that communicate via the Internet. Their goal is to develop useful software that is available for free and that users can change at will. To enable users to change and improve the software, they distribute their software not only in compiled form (that a computer needs to actually run the software), but also in its source code (the lines of code that programmers write). This cooperation breaks through the usual barriers that separate corporate suppliers from their buyers. This may represent the first example where the Internet enables cooperation on a scale that changes market dynamics. This paper studies the interaction between the network dynamics of the open source movement and the dynamics of a commercial software supplier. It makes our first step in identifying conditions that support a successful development of open source software. We focus on one particular set of projects within the open source movement, namely the Linux computer operating system.