Westover Air Reserve Base (IATA: CEF, ICAO: KCEF, FAA LID: CEF) is an Air Force Reserve Command (AFRC) installation located in the Massachusetts communities of Chicopee and Ludlow, near the city of Springfield, Massachusetts. Established at the outset of World War II, today Westover is the largest Air Force Reserve base in the United States, home to approximately 5,500 military and civilian personnel, and covering 2,500 acres (10 km²). Until 2011, it was a backup landing site for the NASA Space Shuttle and in the past few years has expanded to include a growing civilian access airport (Westover Metropolitan Airport) sharing Westover's military-maintained runways. The installation was named for Major General Oscar Westover who was commanding officer of the Army Air Corps in the 1930s.

The host unit is the 439th Airlift Wing (439 AW) of the Fourth Air Force (4 AF), Air Force Reserve Command. Outside of the AFRC command structure, the 439 AW and Westover are operationally gained by the Air Mobility Command (AMC).

Due to its location as one of the few remaining active military air bases in the northeast United States, Westover ARB is transited by many different U.S. military aircraft of all the services.

Westover ARB has the longest runway in Massachusetts.