A hangar is a building or structure designed to hold aircraft or spacecraft. Hangars are built of metal, wood, or concrete. The word hangar comes from Middle French hanghart ("enclosure near a house"), of Germanic origin, from Frankish *haimgard ("home-enclosure", "fence around a group of houses"), from *haim ("home, village, hamlet") and gard ("yard"). The term, gard, comes from the Old Norse garðr ("enclosure, garden").

Hangars are used for protection from the weather, direct sunlight and for maintenance, repair, manufacture, assembly and storage of aircraft.

The Wright brothers stored and repaired their aircraft in a wooden hangar constructed in 1902 at Kill Devil Hills in North Carolina for their glider. After completing design and construction of the Wright Flyer in Ohio, the brothers returned to Kill Devil Hills only to find their hangar damaged. They repaired the structure and constructed a new workshop while they waited for the Flyer to be shipped.

Carl Richard Nyberg used a hangar to store his 1908 Flugan (fly) in the early 20th century and in 1909, Louis Bleriot crash-landed on a northern French farm in Les Baraques (between Sangatte and Calais) and rolled his monoplane into the farmer's cattle pen. Bleriot was in a race to be the first man to cross the English Channel in a heavier-than-air aircraft, and he and set up his headquarters in the unused shed. In Britain, the earliest aircraft hangars were known as aeroplane sheds, and the oldest survivors of these are at Larkhill, Wiltshire. These were built in 1910 for the Bristol School of Flying and are now Grade II* Listed buildings. British aviation pioneer Alliott Verdon Roe built one of the first aeroplane sheds in 1907 at Brooklands, Surrey and full-size replicas of this and the 1908 Roe biplane are on display at Brooklands Museum.

As aviation became established in Britain before World War I, standard designs of hangar gradually appeared with military types too such as the Bessonneau hangar and the side-opening aeroplane shed of 1913, both of which were soon adopted by the Royal Flying Corps. Examples of the latter survive at Farnborough, Filton and Montrose airfields. During World War I, other standard designs included the RFC General Service Flight Shed and the Admiralty F-Type of 1916, the General Service Shed (featuring the characteristic Belfast-truss roof and built-in various sizes) and the Handley Page aeroplane shed (1918).

Sheds built for rigid airships survive at Moffett Field, California; Akron, Ohio; Weeksville, North Carolina; Lakehurst, New Jersey; Santa Cruz Air Force Base in Brazil; and Cardington, Bedfordshire. Steel rigid airship hangars are some of the largest in the world.

Hangar 1, Lakehurst, is located at Naval Air Engineering Station Lakehurst (formerly Naval Air Station Lakehurst), New Jersey. The structure was completed in 1921 and is typical of airship hangar designs of World War I. The site is best known for the Hindenburg disaster, when on May 6, 1937, the German airship Hindenburg crashed and burned while landing. Hangar No.1 at Lakehurst was used to build and store the American USS Shenandoah. The hangar also provided service and storage for the airships USS Los Angeles, Akron, Macon, as well as the Graf Zeppelin and the Hindenburg.

The largest hangars ever built include the Goodyear Airdock measuring 1,175x325x211 feet and Hangar One (Mountain View, California) measuring 1,133 ft × 308 ft × 198 ft (345 m × 94 m × 60 m). The Goodyear Airdock, is in Akron, Ohio and the structure was completed on November 25, 1929. The Airdock was used for the construction of the USS Akron and her sister ship, the USS Macon.