Horse racing is an equestrian sport which has been practiced for many centuries; the chariot races of Roman times are an early example. Nomadic tribesmen of Central Asia have raced horses since early domestication and horse racing has long been an organised sport in many countries throughout history. It is often inextricably associated with gambling.

The breeding, training and racing of horses in many countries is now a significant economic activity, as too is the gambling industry which is largely supported by it. Exceptional horses can win millions of dollars and make millions more by providing stud services, such as horse breeding.

The style of racing, the distances and the type of events varies very much by the country in which the race is occurring, and many countries offer different types of horse races.

Horse racing as a professional sport in the UK can be traced back to the 12th Century after the English knights returned from the Crusades with Arab horses. These horses were bred with English horses to produce the Thoroughbred horse that is the breed of horse used in horse racing in the UK today.

During the reign of Charles II from 1660 to 1685 the King held horse races between two horses on private courses or open fields with prizes awarded to the winners and Newmarket was the venue for the first horse racing meetings in Britain.

Under the reign of Queen Anne during the period 1702-1714 horse races involving several horses on which spectators placed bets took over from match racing and horse racing became a professional sport with racecourses founded throughout England, including Ascot which was founded by Queen Anne in 1711.

While the attention of horse racing fans and the media is focused almost exclusively on the horse's performance on the racetrack, or for male horses possibly its success as a sire, little publicity is given to brood mares. Such is the case of La Troienne, one of the most important mares of the 20th century to whom many of the greatest thoroughbred champions, and dams of champions, can be traced.

In most horse races, not including steeplechases, the pedigree of the horse is one of the factors that allows it to race. In a normal flat race, the horse must have a sire (father) who is a pure thoroughbred and a dam (mother) who is also a pure thoroughbred. In a normal harness race, the horses sire and dam must both be pure standardbred horses.

A stallion who has won many races will usually be put up to stud when he is retired. This means that the owner of a mare can pay to breed his mare to that stallion. The more successful a stallion has been, the more expensive it is to breed the mare. An owner who is serious about racing will strive for the best, and will usually pay the expensive amount, so an owner who has had a successful colt will probably make more money than an owner with a filly.