This chapter first considers the means, from election to selection to nomination, by which IO leaders are (s)elected and the consequences of those methods. It is followed by a discussion on the qualities regarded as necessary for successful tenure, stressing the need for trust, expertise, and legitimacy. It then analyses the three roles that the leaders of IOs, to a greater or lesser extent, must play. They are diplomats dealing with state leaders and talking in international forums. They are politicians negotiating with the state representatives on a daily basis. They are managers heading an often large secretariat. How they balance these roles often determines their capacity to shape the outcomes of their organization.