Andersen Air Force Base (Andersen AFB, AAFB) (IATA: UAM, ICAO: PGUA, FAA LID: UAM) is a United States Air Force base located primarily within the village of Yigo in the United States territory of Guam. The host unit at Andersen AFB is the 36th Wing (36 WG), assigned to the Pacific Air Forces Eleventh Air Force. As a non-flying wing, the 36 WG's mission is to provide support to deployed air and space forces of USAF, foreign air forces to Andersen, and tenant units assigned to the base.

Andersen AFB was placed under the installation management authority of Joint Region Marianas in October 2009, along with Naval Base Guam. The two bases are about 30 miles (48 km) apart at opposite ends of the island. Established in 1944 after the Liberation of Guam as North Field, it is named for Brigadier General James Roy Andersen (1904–1945).

The most important U.S. air base west of Hawaii, Andersen is one of the four Air Force Bomber Forward Operating Locations and the only base in the Western Pacific that can permanently service U.S. heavy strategic bombers, including B-1B, B-2, and B-52 bombers. Andersen is one of two critical bases in the Asia-Pacific region, the other being Diego Garcia in the Indian Ocean. Due to Guam's almost unrestricted airspace and the close proximity of the Farallon de Medinilla Island, a naval bombing range 184 miles (296 km) north, the base is in an ideal training location.

Andersen Air Force Base was established on 3 December 1944, and is named for Brigadier General James Roy Andersen (1904–1945). Andersen graduated from the United States Military Academy in 1926, served at various army installations, and obtained his wings at Kelly Field, Texas, in 1936. During 1943–1944 he served on the War Department General Staff. In January 1945, Andersen was assigned to HQ AAF, Pacific Ocean Area. He died on 26 February 1945 in the crash of a B-24 Liberator aircraft between Kwajalein and Johnston Island while en route to Hawaii.

Andersen Air Force Base's origin begins on 7 December 1941 when Guam was attacked by the armed forces of Imperial Japan in the Battle of Guam (1941) three hours after the Attack on Pearl Harbor. The United States Navy surrendered Guam to the Japanese on 10 December. At the height of the war, approximately 19,000 Japanese soldiers and sailors were deployed to the island. Guam was liberated by the United States Marine Corps' 3rd Amphibious Corps on 21 July 1944, in the Battle of Guam (1944), after a 13-day pre-invasion bombardment.

The Japanese managed to contain the Marines on two beachheads, but their counter-attack failed. The Marines renewed their assault, and reached the northern tip of the island on 10 August 1944. Japanese guerrilla activities continued until the end of the war. Some were holdouts for many years afterwards.

Guam was considered ideal to establish air bases to launch B-29 Superfortress operations against the Japanese Home Islands. The Marianas Islands are about 1,500 miles (2,400 km) from Tokyo, a range which the B-29s could just about manage. Most important of all, it could be put on a direct supply line from the United States by ship. "North Field," as Andersen AFB was first named, was the first air base built in Guam after its liberation. Its construction began in November 1944 and was supported by the United States Navy Seabees. North Field and its co-located Northwest Field was a massive installation, with four main runways, taxiways, revetments for over 200 B-29s, and a large containment area for base operations and personnel.

The first host unit at North Field was the 314th Bombardment Wing, XXI Bomber Command, Twentieth Air Force. The 314th arrived in Guam on 16 January 1945 from Peterson Field, Colorado. The 314th controlled four operational B-29 bomb groups, the 19th (Square M), 29th (Square O), 39th (Square P), and 330th (Square K).