We articulate a teamwork process model of peer justice, defined as a shared perception regarding how individuals who work together within the same unit and who do not have formal authority over each other judge the fairness with which they treat one another. We argue that unit-level judgments of procedural and interpersonal fairness may influence team process, characterized by such things as better communication, better coordination, and more mutual support for members. These team processes, in turn, promote higher team performance and unit-level citizenship behaviors. These ideas were tested among teams of business students working on a semester-long class project. Findings generally supported our theoretical model, attesting to the importance of peer justice. We also found that peer procedural justice strength influenced team outcome variables, including performance, through teamwork processes. The theoretical and practical implications of these findings are discussed.