The Common Security and Defence Policy (CSDP) is the European Union's (EU) course of action in the fields of defence and crisis management, and a main component of the EU's Common Foreign and Security Policy (CFSP).

The CSDP involves the deployment of military or civilian missions to preserve peace, prevent conflict and strengthen international security in accordance with the principles of the United Nations Charter. Military missions are carried out by EU forces established with secondments from the member states' armed forces. The CSDP also entails collective self-defence amongst member states as well as a Permanent Structured Cooperation (PESCO) in which 25 of the 27 national armed forces pursue structural integration. The CSDP structure — headed by the Union's High Representative (HR/VP), Josep Borrell, and sometimes referred to as the European Defence Union (EDU) in relation to its prospective development as the EU's defence arm — comprises:

The EU command & control structures are much smaller than the North Atlantic Treaty Organization's (NATO) Command Structure (NCS), which has been established for territorial defence. It has been agreed that NATO's Allied Command Operations (ACO) may be used for the conduct of the EU's missions. The MPCC, established in 2017 and to be strengthened in 2020, is the EU's first permanent military OHQ. In parallel, the newly established European Defence Fund (EDF) marks the first time the EU budget is used to finance multinational defence projects.

Decisions relating to the CSDP are proposed by the HR/VP, adopted by the FAC, generally requiring unanimity, and then implemented by the HR/VP.