The Australian Cattle Dog is a medium-sized short-coated dog which occurs in two main color forms. The dogs have either brown or black hair distributed fairly evenly through a white coat which gives the appearance of red or blue dogs. They have been nicknamed “Red Heelers” and “Blue Heelers” on the basis of this coloring and their practice of moving reluctant cattle by nipping at their heels. Dogs from a line bred in Queensland, Australia, which were successful at shows and at stud in the 1940s were called “Queensland Heelers” to differentiate them from lines bred in New South Wales and this nickname is now occasionally applied to any Australian Cattle Dog.

While there is a good deal of mythology surrounding the origins of breed, in recent years information technology that enables the manipulation of large databases, and advances in the understanding of canine genetics has allowed a clearer understanding of the Halls Heeler, its dispersal through eastern Australia, and its development into two modern breeds: the Australian Cattle Dog and the Australian Stumpy Tail Cattle Dog.

As with dogs from other working breeds, Australian Cattle Dogs have a good deal of energy, a quick intelligence and an independent streak. They respond well to structured training. They are not aggressive dogs, but they form a strong attachment with their owner and can be very protective of them and their possessions. They are easy dogs to groom and maintain. The most common health problems are deafness and progressive blindness, both hereditary conditions, and accidental injury, otherwise they are a robust breed with a lifespan of twelve to fourteen years. Australian Cattle Dogs participate in a range of activities from obedience, agility and herding competitions, to participating with their owners in hiking, flying disc, and endurance events, and working as therapy or assistance dogs.

Australian Cattle Dogs are sturdy, compact dogs that give the impression of agility and strength. They have a broad skull that flattens to a definite stop between the eyes, with muscular cheeks and a medium length, deep, powerful muzzle. The ears are pricked, small to medium in size and set wide apart, with a covering of hair on the inside. The eyes are oval and dark with an alert, keen expression. The neck and shoulders are strong and muscular; the forelegs are straight and parallel; and the feet round and strongly arched, with small toes and strong nails.

They should have well-conditioned, hard muscles, even when bred for companion or show purposes. Ideally, their appearance is symmetrical and balanced with no individual part of the dog being exaggerated. They should not look either delicate or cumbersome as either characteristic limits agility and endurance which is necessary for a working dog.

Female Australian Cattle Dogs measure approximately 43 to 48 cm (17 to 19 inches) at the withers, and males measure about 46 to 51 cm (18 to 20 inches) at the withers. The dog should be 10% longer than tall, that is, the length of the body from breast bone to buttocks is greater than the height at the withers, as 10 is to 9. Australian Cattle Dogs in good condition weigh approximately 20 to 28 kg (44 to 62 pounds).

Australian Cattle Dogs exhibit two accepted coat colours: red and blue, though the miscolours of chocolate and cream do occur. Blue dogs can be blue, blue mottled or blue speckled with or without black, tan or white markings. Red dogs are evenly speckled with solid red markings. Both colours are born white (save for any solid colored body or face markings) and the red or black hairs grow in as they mature. The distinctive adult colouration is the result of black or red hairs closely interspersed through a predominantly white coat. This is not a roan or merle colouration, but rather the result of the ticking gene. A number of breeds show ticking, which is the presence of color in the white areas with the flecks of color being the same as the basic color of the dog, though the effect depends on other genes that will modify the size, shape and density of the ticking.

In addition to the primary colouration, Australian Cattle Dogs also display some patches of solid or near-solid colour. In both red and blue dogs the most common markings are solid colour patches, or masks, over one or both eyes; a white tip to the tail; a solid spot at the base of the tail, and sometimes solid spots on the body, though these are not desirable in dogs bred for conformation shows. Blue dogs can have tan midway up the legs and extending up the front to breast and throat, with tan on jaws, and tan eyebrows. Both colour forms can have a white 'star' on the forehead called the 'Bentley Mark' after a legendary dog owned by Tom Bentley. Common miscolours in Australian Cattle Dogs include black hairs in a red-coated dog, including the extreme of a black saddle on a red dog; and extensive tan on the face and body on a blue dog, called creeping tan.

The mask is one of the most distinctive features of ACDs. This mask consists of a black patch over one or both eyes (for the blue coat colour) or a red patch over one or both eyes (for the red coat colour). Depending on whether one eye or both have a patch, these are called, respectively, single (or 'half') mask and double (or 'full') mask. Dogs without a mask are called plain-faced. Any of these are correct according to the breed standard, and the only limitation is the owner's preference. In conformation shows, even markings are preferred over uneven markings. Australian Cattle Dogs have a double coat: the short, straight outer 'guard hairs' are protective in nature, keeping the elements from the dog's skin while the undercoat is short, fine and dense.

The breed standard of the Australian, American and Canadian Kennel clubs specify that Australian Cattle Dogs should have a natural, long, un-docked tail. This is because the dogs use their tails as rudders, which provide them with balance and quick reflexes when running or walking. They will often have a solid colour spot at the base of the tail and a white tip. The tail should be set moderately low, following the slope of the back. At rest it should hang in a slight curve, though an excited dog may carry its tail higher. The tail should feature a reasonable level of brush.