A working dog refers to a canine working animal, i.e. a type of dog that is not merely a pet but learns and performs tasks to assist and/or entertain its human companions, or a breed of such origin. In Australia and New Zealand a working dog is one which has been trained to work livestock, irrespective of its breeding.

Within this general description, however, there are several ways in which the phrase is used.

• To identify any dog that performs actions on a regular basis to assist people. In this context, a dog that helps a rancher manage cattle or that performs stunts for a trainer who receives pay for its acts is a working dog, as is a service dog or an assistance dog. This might be in comparison to a companion dog, whose purpose is primarily as a pet.
• To distinguish between dogs that are bred for appearance primarily to win conformation shows and working dogs that are bred primarily for their ability to perform a task. For example, a Border Collie that is a conformation champion is not necessarily a good sheepdog and a Border Collie that is a champion at sheepdog trials might not succeed in show rings for its nonstandard appearance. It is also possible that a specimen may excel in both appearance and performance. In many FCI countries it is impossible for some working breeds' dogs to become conformation champions without having passed adequate breed specific tests measuring their working abilities.

For some breeds, there are separate registries for tracking the ancestry of working and show dogs. For example, in Australia, there are separate registries for working and show Australian Kelpies; the working registry encourages the breeding of any Kelpies with a strong instinct to herd, no matter their appearance or coat color; the show registry encourages breeding only among Kelpies whose ancestors were registered as show dogs and who have only solid-colored coats. Other breeds have just a working dog register, independent of the showing registers; such a breed is the Boerboel — the breeders of this dog consider entry into the AKC for example would damage the dog's genetic working base if it were ever to be bred for the showing.

• As a catch-all for dog breeds whose original purpose was to perform tasks that do not fit into a more specific category of work. For example, the American Kennel Club uses Working Dogs to describe breeds who were originally bred for jobs other than herding or hunting. Such jobs might include pulling carts, guarding and so on. However in practice these 'show' dogs under the AKC are not proper working dogs, and would indeed not be suitable for use as such. Many true working breeds are still very valuable as working dogs, and without them local economies would suffer. An example of such a breed is the Anatolian shepherd without which many sheep would be destroyed for example by wolves, feral domestic dogs, and in Namibia, the cheetah.