Project ventures are an increasingly prevalent organizational form in many industries. The management literature has stressed their flexibility and adaptability advantages. This chapter focuses on the learning implications of the source of flexibility most essential to project ventures: the ability to switch partners during project formation and execution. This partnering flexibility creates opportunities to respond to new knowledge about characteristics of project tasks and project partners. Partnering flexibility, however, also creates learning challenges. The short-term nature of relationships between project partners and the disintegration of the project team after project completion challenges the accumulation and transfer of knowledge to future projects. Beyond the introduction of related learning opportunities and challenges, we identify potential contingency factors in the project context that shape when partner flexibility will have beneficial versus harmful effects. On the organizational level, we propose that project-governing permanent organizations can support project-venture learning. On the industry level, we highlight potential learning benefits of standardized partner roles and coordination practices. Thus, our chapter introduces a multilevel contingency framework for the evaluation of both learning opportunities and challenges of partnering flexibility in project-venture settings. We formulate testable propositions focused on partner-project fit and project performance.