While the Australian Shepherd and Australian Cattle Dog—also called the Blue Heeler—are both admirable herding dogs, they are two distinct breeds developed in different parts of the world. The Australian Shepherd is an American-developed dog with herding ancestors from the areas surrounding Spain, while the Blue Heeler has Australian origins. The Australian Cattle Dog's ancestry includes the Dingo, Dalmatian, and Bull Terrier.
The Australian Shepherd's origin is unclear, but they were not developed in Australia. The breed is thought to share ancestry with herding dogs from Spain's Basque region, and the breed as registered today was developed entirely in North America. Some speculate that the name came from the breed's use in herding sheep imported from Australia, but even that theory is unproven.
The Miniature Australian Shepherd is a separate breed registered by the AKC, though the registry lists the breed as a "Miniature American Shepherd." The Miniature Aussie was developed by breeding smaller-sized Australian Shepherds.
A Teacup or Toy Australian Shepherd is not recognized by the AKC, though they developed by breeding Australian Shepherds with smaller dogs, and they share many of the same characteristics. Because there is no breed standard for the Teacup and Toy varieties, there may be differences in temperament or health.