Dogs and Cat have been selectively bred for thousands of years, sometimes by inbreeding dogs and cats from the same ancestral lines, sometimes by mixing dogs and cats from very different lines. The process continues today, resulting in a tremendous variety of Dog and Cat breeds.
The following list uses a wide interpretation of "breed". Breeds listed here may be traditional breeds with long histories as registered breeds, rare breeds with their own registries, or new breeds that may still be under development. Please see individual articles for more information. See also dog and cat breed and breed.