former aerospace company that was a major U.S. producer of jet fighters, commercial aircraft, and space vehicles.

McDonnell Douglas was formed in the 1967 merger of the McDonnell Aircraft Corporation, founded in 1939, and the Douglas Aircraft Company, established in 1921. The latter's founder, Donald W. Douglas (Douglas, Donald) (1892–1981), first became interested in aviation as a youth while watching the Wright Brothers demonstrate their biplane for the Army in 1909. Later, as a civil engineering assistant at the Massachusetts Institute of Technology's department of aerodynamics, he helped devise one of the first wind tunnels for the testing of aircraft. In 1920 he designed the Cloudster, the first aerodynamically streamlined plane, and founded his company to fill an order for three of the planes for the U.S. Navy.

In 1932 the firm began its landmark DC (Douglas Commercial) series with the DC-1 prototype. The DC-3, the world's first successful commercial airliner, was long a staple on airline routes after its introduction in 1935. During World War II, Douglas converted the DC-3 to military use as the C-47, and this plane became the most widely used transport aircraft of the war. During the war Douglas contributed 29,000 warplanes, one-sixth of the U.S. airborne fleet. After the war the company continued to dominate the commercial air routes with its new DC-6 and in 1953 brought out its most advanced piston-engined airliner, the DC-7, whose range made possible nonstop coast-to-coast service. With the development of commercial jets, however, Douglas began to lag behind Boeing. It was because of its deteriorating financial condition in the 1960s that it sought a merger with McDonnell.

Under its founder James S. McDonnell (1899–1980), that company grew up quickly during World War II and became a major defense supplier. It designed the world's first carrier-based jet fighter and went on to produce such widely used jet fighters as the F-4 Phantom, the A-4 Skyhawk, the F-15 Eagle, and the F-18 Hornet. The company also manufactured launch vehicles and cruise missiles. In 1984 it purchased Hughes Helicopters Inc. from the estate of Howard Hughes. In the 1970s the company began diversifying with the acquisition of companies engaged in data processing, satellite communications, information services, and the manufacture of electronic devices.

The end of the Cold War in the early 1990s resulted in a major contraction of U.S. defense industries. In the wave of business consolidations and mergers that followed, McDonnell Douglas was acquired by The Boeing Company (Boeing Company).