The competitive racing of horses is one of humankind's most ancient sports, having its origins among the prehistoric nomadic tribesmen of Central Asia who first domesticated the horse about 4500 BC. For thousands of years, horse racing flourished as the sport of kings and the nobility. Modern racing, however, exists primarily because it is a major venue for legalized gambling.

Horse racing is the second most widely attended U.S. spectator sport, after baseball. In 1989, 56,194,565 people attended 8,004 days of racing, wagering $9.14 billion. Horse racing is also a major professional sport in Canada, Great Britain, Ireland, Western Europe, Australia, New Zealand, South Africa, and South America.

By far the most popular form of the sport is the racing of mounted THOROUGHBRED horses over flat courses at distances from three-quarters of a mile to two miles. Other major forms of horse racing are harness racing, steeplechase racing, and QUARTER HORSE racing.