Transnational public-private partnerships (PPPs) have become a popular theme in International Relations (IR) research. Such partnerships constitute a hybrid type of governance, in which nonstate actors co-govern along with state actors for the provision of collective goods, and thereby adopt governance functions that have formerly been the sole authority of sovereign states. Their recent proliferation is an expression of the contemporary reconfiguration of authority in world politics that poses essential questions on the effectiveness and the legitimacy of global governance. In this article, we critically survey the literature on transnational PPPs with respect to three central issues: Why do transnational PPPs emerge, under what conditions are they effective, and under what conditions are they legitimate governance instruments? We point to weaknesses of current research on PPPs and suggest how these weaknesses can be addressed. We argue that the application of IR theories and compliance theories in particular opens up the possibility for systematic comparative research that is necessary to obtain conclusive knowledge about the emergence, effectiveness, and legitimacy of transnational PPPs. Furthermore, the article introduces the concept of complex performance to capture possible unintended side effects of PPPs and their implications on global governance.