The apparent success of free/libre open source software (FLOSS) development projects such as Linux, Apache, and many others has raised the question, what lessons from FLOSS development can be transferred to mainstream software development? In this paper, we use coordination theory to analyze coordination mechanisms in FLOSS development and compare our analysis with existing literature on coordination in proprietary software development. We examined developer interaction data from three active and successful FLOSS projects and used content analysis to identify the coordination mechanisms used by the participants. We found that there were similarities between the FLOSS groups and the reported practices of the proprietary project in the coordination mechanisms used to manage task-task dependencies. However, we found clear differences in the coordination mechanisms used to manage task-actor dependencies. While published descriptions of proprietary software development involved an elaborate system to locate the developer who owned the relevant piece of code, we found that “self-assignment” was the most common mechanism across three FLOSS projects. This coordination mechanism is consistent with expectations for distributed and largely volunteer teams. We conclude by discussing whether these emergent practices can be usefully transferred to mainstream practice and indicating directions for future research.