The Chief of the Defence Staff is the highest-ranking military officer in the Spanish Armed Forces and is the principal military advisor to the Prime Minister, the Minister of Defence, the National Defence Council and the National Security Council. It is the fourth military authority of the country after the Monarch, the Prime Minister and the Minister of Defence because the Secretary of State for Defence and the Under-Secretary of Defence do not have military authority.

The Spanish Armed Forces are in charge of guaranteeing the sovereignty and independence of the Kingdom of Spain, defending its territorial integrity and the constitutional order, according to the functions entrusted to them by the Constitution of 1978. They are composed of: the Army, the Air and Space Force, the Navy, the Royal Guard, and the Military Emergencies Unit, as well as the so-called Common Corps.