The title Defence Minister, Minister for Defence, Secretary of Defense, Secretary of State for Defence, Secretary of National Defense or some similar variation, is assigned to the person in a cabinet position in charge of a Ministry of Defence, which regulates the armed forces in sovereign states. The role of a defence minister varies considerably from country to country; in some the minister is only in charge of general budget matters and procurement of equipment; while in others the minister is also, in addition, an integral part of the operational military chain of command.

The Secretary of Defense (SecDef) is the leader and chief executive officer of the Department of Defense, an Executive Department of the Government of the United States of America. The Secretary of Defense's power over the United States military is second only to that of the President. This position corresponds to what is generally known as a Defense Minister in many other countries. The Secretary of Defense is appointed by the President with the advice and consent of the Senate, and is by custom a member of the Cabinet and by law a member of the National Security Council.