| Post: | Under Secretary of the Air Force |
| Flag: | Flag of the Under Secretary of the Air Force.svg |
| Flagsize: | 180px |
| Flagcaption: | Flag of the Under Secretary of the Air Force |
| Insignia: | File:Seal of the United States Department of the Air Force.svg |
| Insigniacaption: | Seal of the Department of the Air Force |
| Department: | Department of the Air Force |
| Incumbent: | Melissa Dalton |
| Incumbentsince: | May 29, 2024 |
| Reports To: | Secretary of the Air Force |
| Style: | Madam Under Secretary The Honorable |
| Seat: | The Pentagon, Arlington County, Virginia, United States |
| Nominator: | The President with the advice and consent of the Senate |
| Termlength: | No fixed term |
| Inaugural: | Arthur S. Barrows |
| Formation: | September 18, 1947 |
| Deputy: | Deputy Under Secretary of the Air Force (Management) and Deputy Chief Management Office |
| Succession: | 17th in SecDef succession by seniority of appointment |
| Salary: | Executive Schedule, level III |
The under secretary of the Air Force (USECAF, or SAF/US), sometimes referred to as the under secretary of the Department of the Air Force,[1] is the second-highest ranking civilian official in the Department of the Air Force of the United States of America, serving directly under the secretary of the Air Force. In the absence of the secretary, the under secretary exercises all the powers and duties of the secretary and serves as acting secretary when the position of secretary is vacant.[2] The under secretary of the Air Force is appointed by the President, by and with the advice and consent of the Senate.
The secretary and under secretary, together with two military officers (the Chief of Staff of the Air Force and the Chief of Space Operations), constitute the senior leadership team of the Department of the Air Force.
The under secretary of the Air Force supervises the following officials: