Since 2003, the European Union has launched more than 20 civilian and military missions across the world. This new role as a crisis manager has not only triggered the creation of more Brussels-based institutions, but has also brought new challenges for the domestic level. The national ministries in the EU member-states are responsible for delivering the civilian or military resources necessary for the implementation of the missions. This article raises the question whether and to what extent the European Security and Defence Policy (ESDP) has affected national administrative structures in terms of both competence allocation and coordination, and examines which factors account for processes of change. The proposed analytical framework builds upon the Europeanization literature and complements the historical institutionalist argument with an actor-based approach emphasizing the preferences and beliefs of the principal political actors. The analytical framework is tested in a case study of Belgium (1999-2007).