The Appaloosa is a horse breed best known for its colorful leopard-spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting patterns overlaid on top of one of several recognized base coat colors. The color pattern of the Appaloosa is of interest to those who study equine coat color genetics, as it and several other physical characteristics are linked to the leopard complex mutation (LP). Appaloosas are prone to develop equine recurrent uveitis and congenital stationary night blindness; the latter has been linked to the leopard complex.
Artwork depicting prehistoric horses with leopard spotting exists in prehistoric cave paintings in Europe. Images of domesticated horses with leopard spotting patterns appeared in artwork from Ancient Greece through the Early modern period; the Nez Perce people of what today is the United States Pacific Northwest developed the original American breed. Appaloosas were once referred to by settlers as the "Palouse horse", possibly after the Palouse River, which ran through the heart of Nez Perce country. Gradually, the name evolved into "Appaloosa".
The Nez Perce lost most of their horses after the Nez Perce War in 1877, and the breed fell into decline for several decades. A small number of dedicated breeders preserved the Appaloosa as a distinct breed until the Appaloosa Horse Club (ApHC) was formed as the breed registry in 1938. The modern breed maintains bloodlines tracing to the foundation bloodstock of the registry; its partially open stud book allows the addition of some Thoroughbred, American Quarter Horse and Arabian blood.
Today, the Appaloosa is one of the most popular breeds in the United States; it was named the official state horse of Idaho in 1975. It is best known as a stock horse used in a number of western riding disciplines, but is also a versatile breed with representatives seen in many other types of equestrian activity. Appaloosas have been used in many movies; an Appaloosa is the mascot for the Florida State Seminoles. Appaloosa bloodlines have influenced other horse breeds, including the Pony of the Americas, the Nez Perce Horse, and several gaited horse breeds.