The United States under secretary of defense for policy (USDP) is a high level civilian official in the United States Department of Defense. The under secretary of defense for policy is the principal staff assistant and adviser to both the secretary of defense and the deputy secretary of defense for all matters concerning the formation of national security and defense policy.

The United States secretary of defense (SecDef) is the head of the United States Department of Defense, the executive department of the U.S. Armed Forces, and is a high-ranking member of the federal cabinet. The secretary of defense's position of command and authority over the military is second only to that of the president of the United States, who is the commander-in-chief. 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.