The United States Automobile Club (USAC) was the primary sanctioning body for open-wheel motor racing in the United States from the mid-1950s until the late 1970s. It was formed to sanction major open-wheel events such as the Indianapolis 500, when that race broke away from Formula One. USAC became the arbiter of rules, car design, and other matters for what it termed Championship automobile racing. This term, which sounds rather generic, in fact became a term of art describing a car built to be used in the highest level of USAC racing. For a while there was a separate series of specifications for Championship cars designed to be run on dirt, rather than paved, tracks.

USAC also became the sanctioning body for many lower levels of motor racing, including sports cars, sprint cars, midget cars, and others. Some of these series were used somewhat as a developmental league for Championship racing.

USAC was not particularly popular with a large segment of drivers, team owners, and crew members, who often found its rules, procedures, and judgements to be rather capricious and arbitrary. This feeling of ill-will came to a head in the late 1970s and led to a break between USAC and most of the Championship team owners and drivers, who formed their own organization, Championship Auto Racing Teams (CART). Unsurprisingly, litigation ensued, in large part over which group had the right to use the term "Championship". This was eventually resolved, in favor of CART.

USAC did not disappear, however, but its influence was obviously greatly lessened. It still continues today as a sanctioning body for some of the lesser levels of motor racing, including the USAC Silver Crown series for tube-framed, alcohol-fueled open-wheel cars racing on dirt and paved ovals, as well as national championships for sprint and midget cars.