Mustang, a small, hardy horse that once ran wild in large herds on the western plains of North America. Mustangs were descended from horses, mainly of Arabian barb stock, brought from Spain, beginning with Hernando Cortez in the 16th century. Horses that escaped from Spanish owners thrived on the grassy plains, and numerous huge bands (called manadas) roamed the far west. Men who made a living catching and taming wild horses were called mustangers.

The availability of mustangs was of great significance to American Indians, permitting them to develop a new culture, one based on buffalo hunting. The Cayuse was a name for a mustang bred by the Cayuse tribe of the Northwest. The appaloosa was a spotted mustang developed by the Nez Percé Indians.

It is estimated that at one time a million or more mustangs roamed the plains. Many were killed to preserve the range for cattle, and others for their flesh, used to make pet foods. Consequently, their numbers dwindled to only a few thousand, but after they were protected by law in the early 1970's their numbers began to increase.