This chapter explores patterns of social and technological interaction that emerge in free/open source software development (F/OSSD) projects found in different research and development communities. F/OSSD is a relatively new way for building and deploying large software systems on a global basis, and differs in many interesting ways from the principles and practices traditionally advocated for software engineering. Hundreds of F/OSS systems are now in use by thousands to millions of end-users, and some of these F/OSS systems entail hundreds-of-thousands to millions of lines of source code. So what's going on here, and how are F/OSSD processes that are being used to build and sustain these projects different?One of the more significant features of F/OSSD is the formation and enactment of complex software development processes performed by loosely coordinated software developers and contributors. These people may volunteer their time and skill to such effort, and may only work at their personal discretion rather than as assigned and scheduled. Further, these developers generally provide their own computing resources, and bring their own software development tools with them. Similarly, F/OSS developers work on software projects that do not typically have a corporate owner or management staff to organize, direct, monitor, and improve the software development processes being put into practice on such projects. But how are successful F/OSSD projects and software development processes possible without regularly employed and scheduled software development staff, or without an explicit regime for software engineering project management? Why will software developers participate in F/OSSD projects? Why and how are large F/OSSD projects sustained? How are large F/OSSD projects coordinated, controlled or managed without a traditional project management team? Why and how might these answers to these questions change over time? These are the core research questions that will be addressed in this chapter.Socio-technical interaction networks (STINs) are an emerging conceptual framework for identifying, organizing, and comparatively analyzing patterns of social interaction, system development, and the configuration of components that constitute an information 2 system [Kling 2003]. STINs provide a scheme for examining the networks of people who work together through interrelated social and technical processes that arise to create the complex information systems and products that collectively constitute ongoing F/OSSD projects.STINs may be seen as the conceptual outgrowth of what historically was called, "sociotechnical systems" (STS) [Scacchi 2004c]. An STS perspective envisions a world of complex organizations that routinely employ technicians/engineers to develop systems for users, where success in developing a system depends on the participation and sustained involvement of the system's users. If people issues in the design, deployment, and evolution of these STS are slighted or ignored, then these systems would be problemati...