Air Force One is the official air traffic control designated call sign for a United States Air Force aircraft carrying the president of the United States. In common parlance, the term is used to denote U.S. Air Force aircraft modified and used to transport the president and a metonym for the primary presidential aircraft, VC-25, although it can be used to refer to any Air Force aircraft the president travels on.

The idea of designating specific military aircraft to transport the president arose during World War II when military advisors in the War Department were concerned about the risk of using commercial airlines for presidential travel. A C-54 Skymaster was then converted for presidential use; dubbed the Sacred Cow, it carried President Franklin D. Roosevelt to the Yalta Conference in February 1945 and was used for another two years by President Harry S. Truman.

The "Air Force One" call sign was created in 1953, after a Lockheed Constellation carrying President Dwight D. Eisenhower entered the same airspace as a commercial airline flight using the same flight number. Since the introduction of SAM 26000 in 1962, the primary presidential aircraft has carried the distinctive livery designed by Raymond Loewy.

Other aircraft designated as Air Force One have included another Lockheed Constellation, Columbine III, three Boeing 707s, introduced in the 1960s and 1970s, and the current Boeing VC-25As. Since 1990, the presidential fleet has consisted of two highly customized Boeing 747-200B (VC-25A) aircraft. The USAF has ordered two Boeing 747-8s to serve as the next presidential aircraft, with designation VC-25B.