Transnational public-private partnerships have become a popular theme in International Relations (IR) research. Such partnerships constitute a hybrid type of governance, in which non-state actors co-govern along with state actors for the provision of public 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. Significant issues are at stake concerning whether transnational public-private partnerships can in fact deliver public goods in an effective and legitimate way. This article surveys the literature with regard to three central issues: It addresses the questions why transnational public-private partnerships emerge, under which conditions they are effective, and under which conditions they are legitimate governance instruments. The article demonstrates that, at present, research on transnational public-private partnerships is theoretically under-informed and suffers from poor research designs. As is pointed out in the course of the article, future research on transnational public-private partnerships could benefit from well-known IR theories on international institutions, from compliance theories in particular. Applying these IR theories to partnerships opens up the possibility for the systematic comparative research that is necessary to obtain conclusive knowledge about transnational public-private partnerships.