The GM A platform (commonly called A-body) was a rear wheel drive automobile platform designation used by General Motors from 1925 until 1959, and again from 1964 to 1981. In 1982, GM introduced a new front wheel drive A platform, and existing intermediate rear wheel drive products were redesignated as G-bodies.

The earliest GM A-bodied based cars shared a common chassis with the Chevrolet Superior, with Pontiac Six replacing Oakland starting in 1926. Oldsmobile also used the A-body for the 1938–48 Series 60. All Chevrolets produced during this period, to include the Chevrolet Master and the Chevrolet Deluxe, and all 1936-39 Pontiacs, the 1940 Pontiac Special, the 1941 Pontiac Deluxe Torpedo and all Pontiac Torpedoes produced from 1942 through 1948 were A-bodies.

From 1949 to 1957, only Chevrolets (150, 210, Bel Air, Del Ray) and Pontiacs (Chieftain, Star Chief, Super Chief) were built on the A-body. These cars were moved to the new B Body shared with some Buicks and Oldsmobiles in 1958, and all truck conversions were replaced by the C/K series in 1960.

The A-body platform returned as an intermediate-sized platform introduced in the 1964 model year for two redesigned and two new mid-sized cars from four of GM divisions. Notable examples include the FR layout Chevrolet Chevelle, Buick Special, Oldsmobile Cutlass and Pontiac Tempest. The A-body cars were the first intermediate-sized cars designed with a full perimeter frame and four-link coil-spring rear suspension, similar to that introduced on full-sized Pontiacs and Oldsmobiles in 1961 and on all other GM full-sized cars in 1965.

The Chevrolet A-body line included the El Camino coupe utility. Two station wagons based on the A-body used stretched wheelbases and raised rear roof sections with skylights: the 1964–1972 Oldsmobile Vista Cruiser and the 1964–69 Buick Sport Wagon.

All A-body cars had a 115 in (292 cm) wheelbase except the stretched-wheelbase wagons, which were 120 in (305 cm).

Some of GM's most successful products in the muscle car era were A-body models, including the Pontiac GTO, Chevrolet Malibu SS, Oldsmobile 442 and Buick GS. From 1964 to 1969, GM Canada produced a special-market version of the Chevelle called the Beaumont, which included Pontiac-type trim and unique front grilles as well as taillight assemblies.

When the A-body cars were introduced in 1964, GM had set a corporate policy prohibiting V8 engines larger than 330 cu in (5.4 L) in these models. However, Pontiac fitted its 389 cu in (6.37 L) V8 in the Lemans to create the GTO — commonly considered the first popular muscle car. Though this violated the 330 cu in limit, Pontiac got around the rules by designating the GTO as a low-volume option package rather than a specific model. The sales success of the 1964 GTO led the corporation to increase the cubic inch limit for 1965 A-body cars to 400 cu in (6.6 L), opening the door for the other three divisions to offer similar muscle cars. The 400 cu in limit for A-body cars, as well as for other GM cars that were smaller than full-sized (with the exception of the Chevrolet Corvette), was continued through the 1969 model year.