The European Union’s Common Security and Defence Policy (CSDP) is scarcely two decades old, yet a considerable and diverse body of literature has emerged during this time. CSDP can best be thought of as the functional crisis management end of the Common Foreign and Security Policy (CFSP), of which it is an integral part. It covers both the military and civilian aspects of crisis management, with the majority of overseas missions being civilian in nature. Yet, it is the growth of the military dimension that has spurred extensive debate about the nature of the EU’s actorness and whether it can still be thought of as a civilian power par excellence. Much of the research has been driven by the application of the main theoretical approaches in international relations to CSDP. The result is an extensive, but occasionally cacophonous, body of literature. Given the relative youth of CSDP there are inevitably gaps in the literature, especially the question of how CSDP relates to other policy fields in the external relations of the EU and whether the “D” in CSDP will remain indefinitely silent.