Scott Air Force Base (IATA: BLV, ICAO: KBLV, FAA LID: BLV) is a United States Air Force base in St. Clair County, Illinois, near Belleville and O'Fallon, 25 miles East of downtown St. Louis. Scott Field was one of thirty-two Air Service training camps established after the United States entered World War I in April 1917. It is part of the Air Mobility Command (AMC), and is also the headquarters of the U.S. Transportation Command, a Unified Combatant Command that coordinates transportation across all the services.

The base is operated by the 375th Air Mobility Wing (375 AMW) and is also home to the Air Force Reserve Command's 932d Airlift Wing (932 AW) and the Illinois Air National Guard's 126th Air Refueling Wing (126 ARW), the latter two units being operationally gained by AMC.

The base currently employs 13,000 people, 5,100 civilians with 5,500 active-duty Air Force, and an additional 2,400 Air National Guard and Reserve personnel. It was announced in June 2014 that two new cybersecurity squadrons will be added to the three currently on base.

Its airfield is also used by civilian aircraft, with civilian operations at the base referring to the facility as MidAmerica St. Louis Airport. MidAmerica has operated as a Joint Use Airport since beginning operations in November 1997. Allegiant Air, the only commercial with scheduled flights at the airport, pulled out of the airport on January 3, 2009, but resumed direct flights to Orlando in 2012.