The Koolie is an Australian dog breed. Specifically, it is a herding dog, a subcategory of working dog. Koolies have existed in Australia since the early 18th century.

The Koolie is a medium-sized dog of varying coat type and colour, although they are generally recognised by their merled coat pattern. Koolies are typically slightly longer than tall and resemble a cross between a Border Collie, a Kelpie and an Australian Cattle Dog - dogs with whom they share Collie bloodline ancestry.

Like the Jack Russell Terrier Club of America, the Koolie Club of Australia defines the breed based on its ability to work rather than on its conformation. Unlike the JRT Club of America, most Koolie breeders refer to this dog as a breed rather than as a type, and assert that it "breeds true".

The Koolie is believed to be descended from the same Collie types that were brought to Australia for the kennels of Thomas S. Hall (an originator of the Australian Cattle Dog breed); some believe that they could be direct descendents of Hall's dogs. This, if true, would make the Koolie the oldest of Australia's breeds.

In 2000, the Koolie Club of Australia was formed to preserve, protect and ethically promote the Koolie breed. Opinion is divided as to whether official recognition would be good for the breed. As of (2006), no bench standard exists and none is expected in the near future.

The Koolie breed is currently not recognized by any kennel club, although judges from the Australian National Kennel Council (ANKC) may judge Koolies in the various sporting trials. In the states of Victoria, New South Wales, and Queensland, registered Koolies may compete in Australian national kennel council-sponsored working, obedience, tracking, jumping and dog agility events by registration on their State's Sporting Register as members of the Koolie Club of Australia.

In April 2005 The Coolie Registry of America (TCR) was created to preserve and maintain the historical records of and begin a registry for Koolies in America, usually known as the German Coolie breed, sometimes called the German Colley/Collie, German Koolie, and/or Kuli. The Coolie Registry of America decided not to change the name of this breed to the Australian Koolie.

In May 2005 The German Coolie Club of America voted and adopted a breed standard for the German Coolies on their registers that are being selectively bred by them in the United States. The club's ultimate goal is to have the Coolie recognized as a breed by the American Kennel Club.

The German Coolies in America are eligible to compete in working sheep dog and cattle dog trials that are sanctioned by the Australian Shepherd Club of America, United States Border Collie Handler's Association, and The American Herding Breed Association. The breed is also eligible to compete in the sports/performance events that are sanctioned by the North American Dog Agility Council and the United States Dog Agility Association.

In May 2006, the Australian Shepherd Club of America, Stockdog Committee, voted to recognize the German Coolie as an ASCA-accepted herding breed.

Graziers, stockmen and dairy farmers across Australia since the days of the earliest settlers to their present day counterparts have typically selected breeds which display the abilities required to meet their working needs. The temperament found in a Koolie is an example of this much sought after ability. The optimal worker possesses a combination of working skills and bonding temperament. There are times when an uninitiated dog owner or a new enthusiast mistakes the Koolie as a shy, reserved or even a timid animal. The Koolies temperament needs to be understood in proper context when one seeks an optimal match of skills and demeanor. The Koolies are intelligent animals and most experienced handlers know well that they need guidance instead of merely being pushed and given praise instead of assigning blame. A steady and supportive approach will be productive, proving the Koolies adaptability in diverse situations when given time. Such is the hallmark it bears and owners will be rewarded through the Koolies diligence in varied roles such as in work situations, sporting activities, loyal service or the time honored role of companionship. Known to be patient, temperate, dedicated, with a strong drive for willingness and devotion, the Koolie is not naturally aggressive but can demonstrate dominance, an untiring enthusiasm to work, and an admirable hardiness when the job or circumstance requires.

DNA testing carried out on 56 Koolies from Australia by Dr.Mark Neff of the University of California at Davis in the USA cleared those bloodlines tested for the presence of the mutant gene mdr1-1, which causes malfunction in the canine multidrug resistance gene; Collie bloodlines were chosen to be tested because they showed a reaction, even death, to chemicals, such as Ivermectin, used in the treatment of intestinal parasites.

Since 2004, the Koolie club of Australia in conjunction with Genetic Science Service of Australia has been undertaking the collection and processing of Koolie DNA, which is being tested for all current Collie diseases and family relationships. To date, the Koolie Club of Australia’s database records that their registered Koolie breed is relatively free of common genetic disorders that are found in recognized pure breeds, thanks to DNA testing. It is general accepted that this is due to the natural breeding selection, which has continued unhindered for over 160 years.

The German Coolie Club of America in concurrence with the Canine Genetic Heritage Project, being conducted at the Center for Veterinary Genetics at the University of California School of Veterinary Medicine, are participating in this research and will be a part of the distinct populations of dogs that will be assembling a comprehensive genetic repository. The Coolies that are tested will be a part of the current DNA bank that adequately reflects the genetic legacy of more than 400 international canine populations that remain unrepresented as a recognized breed. From the information that is assembled from the analyses of the DNA samples, the owners will have a profile of the genetic makeup of the dog. With this profile, futuristically, a person can actively pursue proactive testing for specific genetic defects and diseases.