The GS is a family car manufactured and marketed by Citroën for model years 1970-1986 in saloon and estate bodystyles (1970-1980), over a single generation. The GS received a facelift in 1979 and was subsequently marketed as the GSA in hatchback and estate bodystyles (1979-1986). Almost 2.5 million units were sold.
The GS was voted European Car of the Year for 1971 and was noted as technologically advanced, with class leading comfort, safety and aerodynamics.
The GS filled the gap in Citroën’s range, between the 2CV and Ami economy cars and the luxurious DS executive sedan. The DS had moved significantly upmarket from its predecessor the Citroën Traction Avant, and beyond the finances of most French motorists. Leaving this market gap open for fifteen years allowed other manufacturers entry into the most profitable, high volume market segment in France. This combined with the development costs and new factory for the DS-replacing Citroën CX, the 1974 oil crisis, and an aborted Wankel rotary engine, led Citroën to declare bankruptcy in 1974.

The GS met with instant market acceptance and was the largest selling Citroën model for many years. 1,896,742 GS models and 576,757 GSA models were produced in total.
Unlike the 2CV, Ami, DS and SM, the GS was never officially imported to the USA. A US export model was nearly finished when Citroën withdrew from the US market, with a few dozen cars brought over in 1971 for testing purposes and to be displayed in showrooms. After the project was cancelled, these orphaned cars were sold, mostly to employees of the dealerships. A sealed-beam headlight design was developed, and although never used as intended it was installed in Yugoslav-and Indonesian-assembled models as it made light replacement cheaper and easier.

On 24 August 1970, Citroën launched the GS. The body style was as a Berline (a four-door saloon with three side windows), in a fastback style with a sharp Kammback. The aerodynamics gave the best drag coefficient of any vehicle at the time. On its launch, its main competitors in Europe included the Fiat 128, Ford Escort, Renault 6 and Vauxhall Viva.
Good aerodynamics enabled the car to make the best of the available power, but the car as launched nevertheless drew criticism that it was underpowered. Citroën addressed the issue with the introduction in September 1972, as an option, of a larger 1,222 cc engine. Claimed power increased from 41 kW (55 bhp; 56 PS) to 45 kW (60 bhp; 61 PS), but it was the improved torque that really marked out the more powerful engine, and which enabled the manufacturer, with the larger engined versions, to raise the second gear ratio and the final drive ratio, increasing the vehicle speed per 1,000 rpm from 23 km/h (14.3 mph) to 24.5 km/h (15.2 mph). Larger front brake discs were also fitted.

Visually the GS bore little resemblance to any other car on the market, until the development of the larger Citroën CX in 1974.
The fastback design, with a separate trunk, was controversial – a hatchback layout was considered too utilitarian by CEO Pierre Bercot. The 1974 CX shared this feature. The boot was nevertheless exceptionally large, in part due to the positioning of the spare wheel on top of the engine.