Heads of international organizations (IOs) personify their organization. They are often the only public figures from their organizations who are widely recognized. This chapter seeks to identify the ways that directors-general can exercise their influence. The first section examines the qualities that potential directors-general might require, the way that they reach their positions, and the implications those (s)electoral procedures have for IO leaders. The second section analyses three roles that all heads of IOs play: as managers of diverse multilateral organizations that are sometimes scattered around the globe; as diplomats who represent their organizations in international arenas; and as politicians who must work with member states in the organization. The chapter concludes that how heads of IOs balance these three roles often shape the outcomes of their organizations. They nonetheless operate within constraints. The nature of IO leadership must be contingent, depending on agency and opportunity.