The establishment of the European Security and Defence Policy (ESDP) in 1999 has led to the creation of a whole range of bureaucratic bodies in Brussels and the national capitals. These bodies support the crisis management operations of the European Union. This review article presents the state of the art of academic research on the role of bureaucracy in this recent policy area. It argues that the growing institutional complexity and the constant interaction between actors at the national and European level require scholars to go beyond the dominant approaches of International Relations. Using insights from comparative politics, public administration and multi-level governance, this article considers four important questions: who these civil servants are, why they matter, how they interact, and how they are controlled politically and democratically