The Boeing 720 is a four-engine narrow-body short- to medium-range passenger jet airliner. Developed by Boeing in the late 1950s from the Boeing 707, the 720 has a shorter fuselage and less range. The 720 first flew in November 1959 and the model entered service with launch customer United Airlines in July 1960.

Two primary versions of the aircraft were built. The original 720 with Pratt & Whitney JT3C turbojet engines entered service in 1960, while the improved 720B with Pratt & Whitney JT3D turbofans entered service in 1961. Some 720s were later converted to 720B specification.

Although only 154 were built, the Boeing 720/720B was still profitable due to the low research and development costs of it being a slightly modified version of the 707-120. It was later replaced by the Boeing 727.

Boeing announced its plans to develop a new version of the 707 in July 1957. It was developed from the 707-120 to provide for airline operation for short to medium range flights from shorter runways. The model was originally designated 707-020 before being changed to 720 at the input of United Airlines. Compared to the 707-120, it has four fewer frames in front of the wing, and one less aft, for a total of 8 feet 4 inches (2.54 m) shorter.