A number of high-quality, large-scale, complex software systems, such as Linux, Apache, and Perl, have been successfully produced through the open source software (OSS) paradigm. This fact suggests that effective knowledge coordination must exist within some OSS teams. However, very few studies have attempted to explicate what these coordination mechanisms are. Therefore, this study examines how knowledge is coordinated between the members of an OSS team from the transactive memory system (TMS) perspective. Specifically, we investigate 1) the relation between TMS and the team members’ knowledge coordination behaviors, and 2) the relation between knowledge coordination and the team’s performance. By surveying 61 OSS project teams, the study validates the important role that TMS plays in OSS developers’ knowledge coordination behaviors, which, in turn, have positive influence on their projects’ technical achievement.