European Security and Defence Policy (ESDP) was launched in 1998 with the St. Malo Summit. Since then over 20 Civilian and Military Crisis Management operations were mandated within five years - the start of "European Union peacekeeping". Within the field of European Integration the development of a European Security and Defence Policy marks an important step of the European Union in becoming an international actor. This thesis scrutinizes from a Liberal Intergovernmentalist perspective how the integration in the field of security and defence policy can be explained. The analysis focuses on Germany, France and the United Kingdom. Crucial factors for the development of a European Security and Defence Policy have been the military spending and budgetary constraints, the public support for a European Security and Defence Policy and the Public support for the use of Civilian versus Military Crisis Management.