The Australian Shepherd descends in part from pastoral dogs brought to herd Spanish flocks in North America as early as the 1500s.

[1] There is some speculation that these dogs included the Carea Leonés, a mountain sheepdog that can display the eye color and merle coat found in many contemporary Australian Shepherds.

[2][3] The breed as it is known today developed in California in the 19th century, as a sheep herding dog for Californian shepherds.

[4][3] The Australian Shepherd spread from California throughout the Western United States where it became extremely popular with ranchers who valued the breed's sheep working qualities, as well as their ability to handle cattle and other livestock.

[3] A purely working breed for over a century, the Australian Shepherd was virtually unknown outside of the livestock industry until the mid-20th century when the breed was popularised by Jay Sisler, a rodeo performer, at rodeos across the western states with his Australian Shepherds performing all manner of tricks.

[2][3] From the late-20th century the Australian Shepherd has increasingly been seen in conformation shows and it has become an extremely popular companion dog.

[3][7] The Australian Shepherd is a medium-sized, athletic breed; they typically stand between 18 and 23 inches (46 and 58 cm) and weigh between 35 and 70 pounds (16 and 32 kg).

[2][4] The parent club, the Australian Shepherd Club of America's breed standard states male dogs should stand between 20 and 23 inches (51 and 58 cm) and females between 18 and 21 inches (46 and 53 cm), at the withers; the standard does allow individual animals to exceed these limits slightly.

The white color of double merles is produced due to the lack of melanocytes which provide high potassium levels in the endolymph surrounding the cochlea's hair cells.

[20] The dog has a stride in which its front and back legs cross over, making for an appearance of "on the edge" speed.