The United States Department of the Air Force (DAF) is one of the three military departments within the Department of Defense of the United States of America. The Department of the Air Force was formed on September 18, 1947, per the National Security Act of 1947 (codified into Title 10 of the United States Code) and it is the military department within which the United States Air Force and the United States Space Force are organized.

The Department of the Air Force is headed by the Secretary of the Air Force (SAF/OS), a civilian, who has the authority to conduct all of its affairs, subject to the authority, direction and control of the Secretary of Defense. The Secretary of the Air Force's principal deputy is the Under Secretary of the Air Force (SAF/US). Their senior staff assistants in the Office of the Secretary of the Air Force are five Assistant Secretaries for Acquisition, Financial Management & Comptroller, Installations, Environment & Logistics, Manpower & Reserve Affairs, Space Acquisition and Integration and a General Counsel. The highest-ranking military officers in the department, and senior military advisers to the secretary, are the Chief of Staff of the Air Force and Chief of Space Operations.

By direction of the Secretary of Defense, the Secretary of the Air Force assigns Air Force and Space Force units – apart from those units performing duties enumerated in 10 U.S.C. § 9013 unless otherwise directed – to the combatant commands. Only the Secretary of Defense and the President have the authority to approve a transfer of forces between combatant commands.