This chapter examines the institutional context of the European Union's international relations. EU institutions such as the Council, Commission, European Parliament, and the Court of Justice play substantially different roles depending on the policy area. Such variations reflect differing paths of evolution and the different degrees of integration in different areas of external policy. The chapter first considers how we should think about the roles of institutions before discussing some of the key ideas about the ways in which the EU's institutions work. It then explores how institutions affect three policy areas: the Common Commercial Policy, development cooperation policy and humanitarian aid, and European foreign policy and security cooperation. It also describes four propositions that explain why institutions matter and shows that that change in EU membership and in the institutional arrangements in the global arena has had important implications for the development of the EU's ‘internal’ institutions.