The American Quarter Horse originally bred specifically to race the quarter mile. It is believed to be the world's fastest horse, some having been clocked at 55 mph at the finish line in racing events. It is now equally well known for its performance in rodeos and horse shows. The compact body of the Quarter Horse is well-suited to the speedy maneuvering required in roping, reining, cutting, working cow horse and other stock-horse events. Riders are also known to show Quarter Horses in English and Hunt classes, though these events are more normally dominated by Thoroughbreds and Warmblood crosses. Also known as "America's Horse", the Quarter Horse is the most popular breed in the United States. They can also boast the largest breed society in the world, with over 4 million Quarter Horses registered worldwide.

Breed History
The American colonists began, in the 1690s, to cross imported English horses with Chickasaw Ponies (which originated from Spanish and Barb stock brought over to Americas by the conquistadors). The resulting horse was small, hardy, and quick, and it was used as a work horse during the week, and a race horse on the weekend. The influence of Thoroughbreds like Janus and Matchem contributed crucial genes that developed the colonial "Quarter Mile Horse" into a speedy working man's racer.

As flat racing became popular with the colonists, this horse gained even more popularity as a sprinter. Even when matched against a Thoroughbred, the small horse often won in short, quarter-mile races. As the American Thoroughbred breed was established many colonial Quarter Mile mares were included in the original stud books, starting a long association between the Throughbred breed and what would later become officially known as the "Quarter Horse", accentuating distance it excelled in.

In the 1800s, pioneers heading West wanted a hardy, willing horse. As they forged into unsettled territories they found large herds of feral horses that descended from the Spanish stock Hernan Cortes had introduced into the viceroyalty of New Spain (later to be known as Mexico). As the colonial Quarter Mile Horse was crossed with the native horses of Iberian origin, the pioneers found that this cross had innate "cow sense," and its popularity grew with cattlemen on ranches.

Although working cattle was always the main justification of the ranch horse of the American west the sprint races were always a big part of the weekend entertainment on bush tracks around the country. As a result horses with early speed that also offered an advantage in ranching chores like roping, became important contributors to the breed that was taking shape the western territories. Names like Zantanon, King, Peter McCue, King Plaudit, Top Deck, Vandy and Three Bars are just some of the influential names that brought in more speed emphasizing Thoroughbred bllodlines into the American Quarter Horse breed. As a result, the valued attributes of race horse and show horse competitor were added to its aptitudes on the ranch. Even after the invention of the automobile, the Quarter Horse was never stopped being bred for cattle work. Today large purses have given rise to horses and riders with over a million dollar earnings in stock horse events that are open to all breeds but dominated by American Quarter Horse. At the race track the American Quarter Horse offers a wide assortment of parimutial races with purses as high as two million dollars per race.

This has all been made possible because in 1940, the American Quarter Horse Association (AQHA) was formed to preserve the breed. Before and after the American Quarter Horse formally established itself as a breed it has always benefited from Thoroughbred bloodlines, so as a result their stud book has always remained open to this breed. This is not unusual in the stock horse industry as the Appaloosa has had an open registry to the Thoroughbred, Arabian and American Quarter Horse; the American Paint Stock Horse has had an open registry to the American Quarter Horse; the Azteca is still a composite of the American Quarter Horse and Andalusian breeds; the Criollo has had an open registry to the Chilean Horse. Really the only stock horse breed that has had a closed registry since it was first officially started in 1893 is the Chilean Horse.

Today, Europe has been importing Quarter Horses at nearly the same rate North America imports warmbloods. Germany and Italy in particular have been drawn to this breed. The horses are not only ideal for ranch and cattle work, barrel racing, and gymkhana events, but have also been trained to international levels of dressage and are generally very good jumpers. Although this breed started as America's Horse it is rapidly becoming the World's Horse. The second highest registry of Quarter Horses takes place in Brazil and Australia is not far behind. With the internationalization of the discipline of reining and its acceptance as one of the official seven events on the World Equestrian Games, now there is a growing interest in Quarter Horses the world over. Countries like Japan, Switzerland and Israel that did not have a traditional stock horse industry have been lured to compete on sturdy American Quarter Horses in their own country and abroad.

Breed Characteristics
There are as many types of Quarter Horses as there are types of work they do. However, there are two main body types: the stock type and the running type. The stock horse type is shorter, more compact, stocky and very well muscled, yet agile. The running Quarter Horse is lighter, similar to a Thoroughbred, and is built to sprint.

Quarter Horses shown in hand "at halter" have a heavy-bodied appearance due to their incredibly muscular build, and small typey heads that usually have large jowls and refined muzzles. Reiners and cutters are smaller, with cat-like, quick movement and very powerful hindquarters. Western pleasure horses have a more level topline and smooth gaits. Quarter Horse racehorses have long legs and are much leaner than their "stock horse" counterparts. The show hunter type is similar to the running type Quarter Horse although many are even of a taller and thinner phenotype. However, all Quarter Horses have speed, stamina, power, and a great willingness to please.

Quarter Horses come in all colors, except spotted or pinto colors, with sorrel and bay being the most common color. They usually stand 14-16 hands high although there are exceptions that maybe as tall as 17 hands. The breed stipulates registerable height.

The Thoroughbred breed is an accepted outcross for Quarter Horses; the major Quarter Horse breed registry (the largest horse registry in the world), the American Quarter Horse Association, accepts Quarter Horse/Thoroughbred crosses into the registry as "Appendix Quarter Horses." These animals are popular for Quarter Horse Racing and for Jumping and Hunter events. When meeting a series of conformational and performance criteria these Appendix Quarter Horses can obtain permanent registrations numbers. Since American Quarter Horse/Thoroughbred crosses continue to have an opportunity to enter the official registry of the American Quarter Horse breed this is creating a continual gene flow from the Thoroughbred breed into the American Quarter Horse breed which has been influential in altering many of the characteristics that typified the breed in the early years of its formation.