The Pontiac GTO is a front-engine, rear-drive, two-door, and four-passenger automobile manufactured and marketed by the Pontiac division of General Motors over four generations from 1963 until 1974 in the United States — with a fifth generation made by GM's Australian subsidiary, Holden, for the 2004 through 2006 model years.

The first generation of the GTO is credited with popularizing the muscle car market segment in the 1960s. Some consider the Pontiac GTO to have started the trend with all four domestic automakers offering a variety of competing models.

For the 1964 and 1965 model years, the GTO was an optional package on the intermediate-sized Pontiac LeMans. The 1964 GTO vehicle identification number (VIN) started with 22, while the 1965 GTO VIN began with 237. The GTO was designated as a separate Pontiac model from 1966 through 1971 (VIN 242...). It became an optional package again for the 1972 and 1973 intermediate LeMans. For 1974, the GTO was an optional trim package on the compact-sized Ventura.

The GTO model was revived for the 2004 through 2006 model years as a captive import for Pontiac, a left-hand drive version of the Holden Monaro, itself a coupé variant of the Holden Commodore.

In early 1963, General Motors management banned divisions from involvement in auto racing. This decision followed the 1957 voluntary ban on automobile racing that the Automobile Manufacturers Association instituted. By the early 1960s, Pontiac's advertising and marketing approach was heavily based on performance. With GM's ban on factory-sponsored racing, Pontiac's managers emphasized street performance.

In his autobiography Glory Days, Pontiac chief marketing manager Jim Wangers, who worked for the division's contract advertising and public relations agency, states that John DeLorean, Bill Collins, and Russ Gee were responsible for the GTO's creation. It involved transforming the upcoming second-generation Pontiac Tempest (which reverted to a conventional front-engine with front transmission configuration) into a sporty car, with a larger 389 cu in (6.4 L) Pontiac V8 engine from the full-sized Pontiac Grand Prix hardtop coupe in place of the standard 326 cu in (5.3 L) V8. By promoting the big-engine option as a unique high-performance model, they could appeal to the youth market (which had also been recognized by Ford Motor Company's Lee Iacocca, who was preparing the Ford Mustang variant of the second-generation Ford Falcon compact).

The GTO disregarded GM's policy limiting the A-body intermediate line to a maximum engine displacement of 330 cu in (5.4 L). The development team discovered a loophole in the policy that did not restrict the offering of large engines as an option. Pontiac general manager Elliot "Pete" Estes approved the new model with sales manager Frank Bridge limiting initial production to 5,000 cars.

The name, GTO was inspired by the Ferrari 250 GTO. The moniker is an Italian abbreviation for Gran Turismo Omologato ("grand tourer homologated"), designating being certified by the FIA for racing in the grand tourer class as a production car with at least a hundred units made.