In this review article we explore the growing body of literature on the subject of trust in the field of international relations. We argue that the international level represents a unique challenge for trust research. This is so because some of the most pressing problems facing the world today require the development of trusting relationships internationally. In addition, the international environment is structurally different from domestic or personal relations on which much of the trust literature has focused so far. We identify three main strands of trust literature in international relations – rationalist, social and psychological. We not only note the contributions these have made to understanding the role of trust internationally, but also highlight areas where more research is needed. Particularly, we argue that this includes theorising processes of trust-building, the identification of trusting relationships and the development of a normative case for trust among states.