In this chapter we summarize the latest results from an ongoing study examining Free/Open Source Software (F/OSS) Development communities as self-organizing systems. Using publicly available data about projects, developers, and their relationships at F/OSS hosting sites such as SourceForge, we have found the existence of several power-law relationships, which is consistent with the contention that F/OSS communities are self-organizing systems. The F/OSS community is modeled as a collection of ad hoc, social networks consisting of heterogeneous agents, self-organizing into projects and clusters of projects. A computer simulation of the F/OSS community model is developed using SWARM, an agent-based simulation toolkit. Empirical data is used to parameterize the simulation, which in turn is used to investigate a social psychological model of communication and team effectiveness in F/OSS projects.