Collies form a distinctive type of herding dogs, including many related landraces and standardized breeds. The type originated in Scotland and Northern England. Collies are medium-sized, fairly lightly-built dogs, with pointed snouts. Many types have a distinctive white color over the shoulders. Collies are very active and agile, and most types of collies have a very strong herding instinct. Collie breeds have spread through many parts of the world, and have diversified into many varieties, sometimes mixed with other dog types.

A herding dog, also known as a stock dog or working dog, is a type of dog that either has been trained in herding livestock or belongs to one of the breeds that were developed for herding. A dog specifically trained to herd sheep is known as a sheep dog or shepherd dog.