The Douglas DC-8 (sometimes McDonnell Douglas DC-8) is a narrow-body airliner built by the American Douglas Aircraft Company. After losing the May 1954 USAF tanker requirement to the Boeing KC-135, Douglas announced in July 1955 its derived jetliner project. In October 1955, Pan Am made the first order along with the competing Boeing 707, and many other airlines followed. The first DC-8 was rolled out in Long Beach Airport on 9 April 1958 and flew for the first time on 30 May. FAA certification was achieved in August 1959 and the DC-8 entered service with Delta Air Lines on September 18.

The six-abreast, low wing airliner was a four-engined jet aircraft, the initial variants are 151 ft (46 m) long. The DC-8-10 was powered by Pratt & Whitney JT3C turbojets and had a 273,000 lb (124 t) MTOW, the DC-8-20 had more powerful JT4A turbojets for a 276,000 lb (125 t) MTOW. The intercontinental models had more fuel capacity and up to 315,000 lb (143 t) MTOW, powered JT4As for the Series 30 and by Rolls-Royce Conway turbofans for the Series 40. The Pratt & Whitney JT3D powered the later DC-8-50 and freighters versions reached a MTOW of 325,000 lb (147 t).

The improved Series 60 was announced in April 1965. The DC-8-61 was stretched by 36 ft (11 m) for 180–220 seats in mixed-class and a MTOW of 325,000 lb (147 t). It first flew on March 14, 1966, was certified on September 2, 1966, and entered service with United Airlines in February 1967. The long-range DC-8-62 followed in April 1967, stretched by 7 ft (2.1 m), could seat up to 189 passengers over 5,200 nmi (9,600 km) with a larger wing for a MTOW up to 350,000 lb (159 t). The DC-8-63 had the long fuselage and the enlarged wing, freighters MTOW reached 355,000 lb (161 t).

The DC-8 was produced until 1972 with 556 aircraft built. It was superseded by larger wide-body airliners including Douglas' DC-10. In 1975, the Series 70 retrofit was proposed with the quieter and more fuel-efficient CFM56 turbofan. Some re-engined freighters are still in use.