The Koolie (also known as the Australian Koolie or by the historic misnomer "German Coolie") is an Australian dog breed. The Koolie is a working or herding dog which has existed in Australia since the early 19th century when it was bred from imported British working dogs. Robert Kaleski, in an article on Cattle Dogs in the August 1903 issue of the Agricultural Gazette of New South Wales, describes the "Welsh heeler or merle, erroneously known as the German collie," as a "blue-gray dog about the size and build of a smooth-haired collie, generally with wall eyes." The British background predominated in the dogs that came to be associated with the "German collie" name.

There is substantial variation in the Koolie population, as Koolies were bred to exhibit different characteristics in different regions. The breed is based on its ability to work rather than on its conformation. However, most Koolie breeders refer to the Koolie as a breed rather than as a type, and assert that it "breeds true", with various types or strains.

The Koolie is a "herding dog", one which has a natural instinct to circle widely round sheep and bring them back to their owner. Koolies are known as silent, upright, working dogs. They are used for herding sheep and also for quiet careful work at close quarters at lambing time or for "shedding" (cutting out) sheep.

With the demand for farming dogs no longer being what it was, the Koolie has proven its worth in many other fields where it is renowned for its sensitivity, athleticism and obedience, excelling in agility, tracking, therapy, disability & emotional support service, and as the ultimate outdoor & family companion, providing they are well trained.

The Koolie is as diverse as the country it originates from, Australia. In the north of Queensland and New South Wales they are tall, medium boned and agile, bred for mustering cattle over many miles. In New South Wales, they are thicker set and shorter to flush low lying cattle from the dense bush and gullies. In Victoria, one finds the smallest variety of the Koolie, primarily used for sheep. Koolies are bred to meet the needs of the stockman, grazier and farmer; all agile, all with the same ability to adapt to any situation, all with a strong willingness drive. Male Koolies stand between 17 and 20 inches (43 to 51 cm) tall at the shoulder, while females typically measure slightly smaller, ranging from 16 to 19 inches (41 to 48 cm). Most often, they are seen in the merle coat pattern, but can exhibit any combination of colour and coat lengths. The solid red or black Koolie are often mistaken for Kelpies, and some bi-coloured Koolie have been taken for Border Collies by the general public. As all of these breeds share Collie ancestry, they resemble each other.

The Koolie coat ranges from short/smooth (like that of the original blue merle Collies from Scotland), short (like a working Kelpie), medium and, not common, long (like the show Border Collie). Koolies are typically slightly longer than tall. The majority of owners prefer the short/smooth coats as they do not pick up grass seed, and are very easy to maintain, with the occasional swim to keep the coat glossy and free of parasites.

Koolie colours are classed as Solid or Merle.

A Solid does not show any Merle pattern, and can come in any colour such as all one colour black, red, chocolate, cream, dilute red (lilac), dilute black (blue), with tan points, black & white, dilute & white or red & white, or "Tri" -solid red or black, with white markings, normally with brown points.