American open-wheel car racing

American open-wheel car racing, generally and commonly known as Indy car racing, is a category of professional automobile racing in the United States. As of 2025, the top-level American open-wheel racing championship is sanctioned by IndyCar and is known as the IndyCar Series. Competitive events for professional-level, open-wheel race cars have been conducted under the auspices of various sanctioning bodies, and traces it roots as far back as 1902. A season-long, points-based, National Championship of drivers has been officially recognized in 1905, 1916, and each year since 1920 (except for a hiatus during WWII). As such, for many years, this discipline of motorsports was known as Championship car racing (or Champ car racing for short). That name has fallen from use, and the term Indy car racing (derived from the Indy 500) has become the preferred moniker.

The machines, typically referred to as "Indy cars", are a formula of single-seat, open cockpit, open-wheel, purpose-built race cars. They compete on a variety of circuits, including ovals, road courses, street circuits, and combined road courses. The most famous and most important event of the season is the Indianapolis 500, held at the Indianapolis Motor Speedway on Memorial Day weekend in late May. Over the decades, Indy cars have been generally similar to those in Formula One, though there are important differences. Though the IndyCar Series is American-based, international races have occasionally been held, in such places as Canada, Mexico, Brazil, Japan, and Australia, as well as Europe.

This form of racing experienced considerable growth and popularity in the decades after World War II. The "Golden Era" of the front-engined roadsters was followed by a decade of innovation and transition in the 1960s. By the late-1960s and early-1970s, the cars had rapidly evolved to rear-engined, formula-style machines. Speeds climbed on the superspeedways to over 200 miles per hour (320 km/h), while international participation also increased. The sport saw much success, exposure, and popularity particularly during the 1980s–1990s under the sanctioning of Championship Auto Racing Teams (CART). Organizational disputes in 1979 and 1996 split participants and the fanbase among two separate competing series. The sport was re-unified in 2008, and in late 2019, IndyCar and the Indianapolis Motor Speedway were bought by Roger Penske and Penske Entertainment.

The national championship was sanctioned by the Contest Board of the American Automobile Association (AAA). The AAA first sanctioned automobile motorsports events in 1902. At first it used the rules of the Automobile Club of America (ACA), but it formed its own rules in 1903. It introduced the first track season championship for racing cars in 1905. Barney Oldfield was the first champion. No official season championship was recognized from 1906 to 1915, however, many races were held. Official records regard 1916 as the next contested championship season. Years later, retroactive titles were named back to 1902. These post factum seasons (1902–1904, 1906–1915, and 1917–1919) are considered unofficial and revisionist history by accredited historians.

Racing did not cease in the United States during WWI, but the official national championship was suspended. The Indianapolis 500 itself was voluntarily suspended for 1917–1918 due to the war. In 1920, the championship officially resumed, and despite the difficult economic climate that would later follow, ran continuously throughout the Depression. Shortly after the attack on Pearl Harbor, all auto racing was suspended during World War II. From 1942 to 1945 no events were contested, banned by the U.S. government primarily on account of rationing. Racing resumed in full in 1946. The 1946 season is unique, in that it included six Champ Car events, and 71 "Big Car" races, as organizers were initially unsure about the availability of cars and participation.

AAA ceased participation in auto racing at the end of the 1955 season. It cited a series of high-profile fatal accidents, namely Bill Vukovich during the 1955 Indianapolis 500, and the 1955 Le Mans disaster.

Through 1922 and again from 1930 to 1937, it was commonplace for the cars to be two-seaters, as opposed to the aforementioned standard single-seat form. The driver would be accompanied by a riding mechanic (or "mechanician").

The national championship was taken over by the United States Auto Club (USAC), a new sanctioning body formed by the then-owner of the Indianapolis Motor Speedway, Tony Hulman. Championship racing continued to grow in popularity in a stabilized environment for over two decades, with the two traditional disciplines of paved oval tracks and dirt oval tracks. During the 1950s, front-engined "roadsters" became the dominant cars on the paved oval tracks, while "upright" Champ Dirt Cars continued to dominate on dirt tracks. In the 1960s, drivers and team owners with road racing backgrounds, both American and foreign, began creeping into the series and the paved oval track cars evolved from front-engine "roadsters" to rear-engine formula-style racers. Technology, speed, and expense climbed at a rapid rate. The schedule continued to be dominated by oval tracks, but a few road course races were added to assuage the newcomers. Dirt tracks were dropped from the national championship after 1970.