In exploring the leadership practices of chief executives of intergovernmental organizations (IGOs), this article finds that IGO leaders recognize themselves as agents and as brokers. This article produces findings from a multiple-case study of the executive leadership of NATO from 1995 to 1999 and of the EU Common Foreign and Security Policy from 1999 to 2009. The relationship between member states and the IGO leader can be conceived as a principal–agent relationship where the agent plays a central role in framing a common vision and strategies, facilitating member states’ involvement in the strategizing process, and mobilizing external and internal support. I depart from a restrictive principal–agent conceptualization of the relationship because I do not envision it as conflictive, but rather as collaborative.