The Aérospatiale Gazelle (company designations SA 340, SA 341 and SA 342) is a five-seat helicopter developed and initially produced by the French aircraft company Sud Aviation, and later by Aérospatiale. It is the first helicopter to feature a fenestron tail instead of a conventional tail rotor, as well as being the first helicopter to be adapted for single-pilot operations under instrument flight rules.

The Gazelle was developed during the 1960s as a successor to the Alouette II as well as to meet a French Army requirement for a new lightweight observation helicopter. The Gazelle is considerably larger than the preceding Alouette series, yet is still powered by a single Turbomeca Astazou turbine engine. Innovations in the design of the Gazelle, aside from the fenestron, included an emphasis on minimal maintenance requirements from the onset of development and the use of a semi-rigid composite rotor system, the latter having required considerable development time. In February 1967, France and the United Kingdom inked a cooperation agreement, which would see Westland Aircraft produce the Gazelle on British soil and partner with Sud Aviation on future refinements and upgrades to the Gazelle. On 7 April 1967, the Gazelle performed its maiden flight.

The first operational Gazelles were introduced in 1971. Initially, manufacturing lines for the type were established in both France and Britain but later on, it was also manufactured under license by SOKO in Yugoslavia and the Arab British Helicopter Company (ABHCO) in Egypt. Multiple armed variants, orientated towards roles such as anti-tank gunship (SA 342M), light support (SA 341F), and anti-air variants were promptly produced for various branches of the French armed forces. The Gazelle was flown by all branches of the British armed forces—the Royal Air Force, Royal Navy (including in support of the Royal Marines) and the British Army in a variety of roles. The Gazelle has been procured and operated by a wide range of export customers. While it has been typically operated in a military capacity to perform light transport, scouting, and light attack missions, the Gazelle has also seen use with civil operators as well.

During its lengthy service life, the Gazelle has participated in numerous conflicts around the world, including by Syria during the 1982 Lebanon War, by Rwanda during the Rwandan Civil War in the 1990s, and by numerous participants on both sides of the 1991 Gulf War. By the twenty-first century, many operators were in the process of replacing the Gazelle with newer rotorcraft; in French service, the Gazelle has been supplanted as an attack helicopter by the larger and more modern Eurocopter Tiger, but remained active for some time in the scout helicopter role. Numerous operators have elected to upgrade their rotorcraft for continued service, the type still being in use with multiple countries as of 2024. Production ended in 1996.

In 1966, Sud Aviation began working on a light observation helicopter to replace its Alouette II with seating for five people. The Gazelle originated in a French Army requirement for a lightweight observation helicopter intended to replace the Aérospatiale Alouette III; early on in the aircraft's development, the decision was taken to enlarge the helicopter to enable greater versatility and make it more attractive for the export market.

Early on, the Gazelle attracted British interest, which resulted in a major production work share agreement between Sud Aviation and Westland. Under the terms of the agreement, Westland would have a 65% work share in the manufacturing of the units destined for the British military, and be a partner to Sud Aviation on further refinements and upgrades to the Gazelle. The deal, signed in February 1967, allowed the production in Britain of 292 Gazelles and 48 Sud Aviation SA 330 Puma medium transport helicopters ordered by the British armed forces. In return, Sud Aviation was given a work share in the manufacturing programme for the 40 Westland Lynx naval helicopters for the French Navy. Ultimately, Westland would produce a total of 262 Gazelles of various models, mainly for various branches of the British armed forces but Gazelles for the civil market were also produced.

The first prototype SA 340 flew for the first time on 7 April 1967, it initially flew with a conventional tail rotor taken from the Alouette II. The tail was replaced in early 1968 with the distinctive fenestron tail on the second prototype. Four SA 341 prototypes were flown, including one for British firm Westland Helicopters. On 6 August 1971, the first production Gazelle conducted its first flight. On 13 May 1967, a Gazelle demonstrated its speed capabilities when two separate world speed records were broken on a closed course, achieving speeds of 307 km/h over 3 kilometres and 292 km/h over 100 kilometres.

In service with the French Army Light Aviation (ALAT), the Gazelle was used primarily as an anti-tank gunship (SA 342M) armed with Euromissile HOT missiles. A light support version (SA 341F) equipped with a 20 mm cannon is used as well as anti-air variants carrying the Mistral air-to-air missile (Gazelle Celtic based on the SA 341F, Gazelle Mistral based on the SA 342M). The latest anti-tank and reconnaissance versions carry the Viviane thermal imagery system and so are called Gazelle Viviane. The Gazelle is being replaced in frontline duties by the Eurocopter Tiger, but will continue to be used for light transport and liaison roles.