The United States Air Force (USAF) is the air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its origins to 1 August 1907, as a part of the United States Army Signal Corps, the USAF was established by transfer of personnel from the Army Air Forces with the enactment of the National Security Act of 1947. It is the second youngest branch of the United States Armed Forces and the fourth in order of precedence. The United States Air Force articulates its core missions as air supremacy, global integrated intelligence, surveillance and reconnaissance, rapid global mobility, global strike, and command and control.

The Department of the Air Force, which serves as the USAF's headquarters and executive department, is one of the three military departments of the Department of Defense. The Department of the Air Force is headed by the civilian secretary of the Air Force, who reports to the secretary of defense and is appointed by the president with Senate confirmation. The highest-ranking military officer in the Air Force is the chief of staff of the Air Force, who exercises supervision over Air Force units and serves as one of the Joint Chiefs of Staff. As directed by the secretary of defense and secretary of the Air Force, certain Air Force components are assigned to unified combatant commands. Combatant commanders are delegated operational authority of the forces assigned to them, while the secretary of the Air Force and the chief of staff of the Air Force retain administrative authority over their members.

Along with conducting independent air operations, the United States Air Force provides air support for land and naval forces and aids in the recovery of troops in the field. As of 2020^[update], the service operates approximately 5,500 military aircraft and approximately 400 ICBMs. The world's largest air force, it has a $179.7 billion budget and is the second largest service branch of the U.S. Department of Defense, with 321,848 active duty airmen, 147,879 civilian personnel, 68,927 reserve airmen, 105,104 Air National Guard airmen, and approximately 65,000 Civil Air Patrol auxiliaries.

According to the National Security Act of 1947 (61 Stat. 502), which created the USAF:

Section 9062 of Title 10 US Code defines the purpose of the USAF as:

The five core missions of the Air Force have not changed dramatically since the Air Force became independent in 1947, but they have now evolved and are articulated as air superiority, global integrated ISR (intelligence, surveillance and reconnaissance), rapid global mobility, global strike, and command and control. The purpose of all of these core missions is to provide what the Air Force states as global vigilance, global reach, and global power.

Air superiority is "that degree of dominance in the air battle of one force over another which permits the conduct of operations by the former and its related land, sea, air, and special operations forces at a given time and place without prohibitive interference by the opposing force" (JP 1-02).

Offensive Counter-Air (OCA) is defined as "offensive operations to destroy, disrupt, or neutralize enemy aircraft, missiles, launch platforms, and their supporting structures and systems both before and after launch, but as close to their source as possible" (JP 1-02). OCA is the preferred method of countering air and missile threats since it attempts to defeat the enemy closer to its source and typically enjoys the initiative. OCA comprises attack operations, sweep, escort, and suppression/destruction of enemy air defense.