Air Force One is the call sign of any U.S. Air Force plane carrying the President of the United States. Though only officially called Air Force One while the President is aboard, the two custom Boeing 747-200B planes that the President uses to fly are commonly referred to as Air Force One. Air Force One can carry up to 70 passengers and 26 crew members, and over time has become a symbol of the American presidency.

On April 27, 2009, the back-up Air Force One plane flew at a low altitude near lower Manhattan for the purpose of a photo-op. Fearing another terrorist attack, people working in buildings near the flight path rushed outside. Mayor Michael Bloomberg was also uninformed of the exercise and expressed anger that he wasn't told by White House officials. The White House did issue an apology later in the day.CBSNews: Katie Couric's Notebook: Air Force One (April 28, 2009)

In 1943 Franklin D. Roosevelt became the first active President to fly in a plane, as he traveled overseas in a Boeing 314 to attend a World War II peace conference. Following the trip the U.S. Air Force decided to designate a plane specifically designed for presidential air travel and selected a C-87A Liberator Express with a call sign of Guess Where Two. Due to the crash of another C-87A plane, the presidential plane was switched again, this time to a C-54 Skymaster with the call sign of Sacred Cow. It was this C-54 Skymaster that President Roosevelt famously installed a retractable elevator so he could board with his wheelchair. As President Truman entered office he upgraded the C-54 Skymaster to a C-118 Liftmaster and changed the call sign to Independence.

It was during the presidency of Dwight D. Eisenhower in which the call sign of Air Force One was officially introduced as a result of an incident in which another plane was using the same call sign as the President's plane. Eisenhower introduced additional planes to be used for presidential air travel and became the first president to have an air to ground telephone in Air Force One. In 1958 the Air Force added three Boeing 707's to the presidential plane fleet, and these would remain in service (along with upgraded Boeing 707's) until 1990. During President Reagan's term he ordered the replacement of the Boeing 707's with new Boeing 747's. The first 747 was delivered in 1990 during the presidency of George H. W. Bush. The Boeing 747 fleet is still in use today, but may be retired in 2010 after 20 years in service.