The under secretary of defense for personnel and readiness, or USD (P&R) is a high-ranking civilian position in the Office of the Secretary of Defense (OSD) within the United States Department of Defense responsible for advising the secretary and deputy secretary of defense on recruitment, career development, pay and benefits, and oversight of the state of military readiness. The under secretary is appointed from civilian life by the president and confirmed by the Senate to serve at the pleasure of the President.

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.