Partnering as a concept has matured in its application and many empirical studies provide evidence of its impact on project performance beyond the rather prescriptive and anecdotal claims of earlier cookbooks on the subject. What has remained elusive, however, is a guiding theory on partnering. Drawing on the literature, partnering is explained within the framework of intergroup contact theory and teamwork in organizations. More specifically, partnering has the potential to create the essential conditions for optimal intergroup contact and hence, to reduce bias and increase cooperation among construction project workgroups and, consequently, favorably impact on project performance. Demonstrating a close fit with the published literature on partnering provides useful support for the proposed model. The model can clearly help project managers to focus their attention on the necessary aspects of workgroup processes that lead to high cooperation and performance.