in the United States, the racing of horses at great speed for short distances on a straightaway course, originally a quarter of a mile, hence the name. Quarter-horse racing was begun by the early settlers in Virginia shortly after Jamestown was established in 1607. Traditionally the course was 0.25 mile (400 m), using whatever pathways were available or could be cut through the forests, and later a street of a settlement.

Organized quarter-horse racing began in the 1940s and thereafter came to be held on about 100 tracks in the United States, mainly in the West. There are 11 officially sanctioned race distances from 220 to 870 yards (201 to 796 m). Races of 550 yards or less are run on straight courses; one or part of one turn may be used in the lengthier (“hook”) races. Rules and procedures are basically the same as those for Thoroughbred horse races, but timing is to the nearest ¹/₁₀₀ second from a standing start. The Triple Crown of quarter-horse racing includes the Kansas Futurity, held in June, the Rainbow Futurity, held in July, and the All-American (American Quarter Horse) Futurity, held in September on Labor Day, all at Ruidoso Downs, New Mexico.

Long recognized as a distinct type, quarter horses are known for their ability to start quickly and sprint swiftly, producing close contests with many photo finishes. The breed originated in Virginia from a Thoroughbred stallion, Janus, and native mares.