The United States Automobile Club (USAC) is an open-wheel auto racing sanctioning body. From 1956 to 1978 the USAC organised the United States National Championship, and from 1956 to 1998 it organised the Indianapolis 500.

It was formed when the American Automobile Association (AAA) withdrew from auto racing following the 1955 Le Mans disaster. 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. After an attempt to form a new championship, called the Championship Racing League (CRL), was vetoed by Indianapolis Speedway management, the USAC and CART eventually settled into a relatively pieceful co-existence, with the USAC continuing to sanction to Indianapolis 500, and CART including the race in its schedule.

While the USAC did not disappear, its influence was 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.