border collie, breed of medium-sized, sheepherding dog developed in the British Isles. It stands about 18 in. (45.7 cm) high at the shoulder and weighs from 30 to 45 lb (13.6–20.4 kg). Its double coat consists of a soft, fuzzy underlayer and a harsh, very dense, wavy or slightly curly topcoat of varying lengths. Its color is black with white around the neck and on the chest, face, feet, and tip of tail. Bred for many years exclusively to develop its herding instinct, the border collie is unsurpassed as a sheep dog and has been used with equal success for herding cattle, swine, and poultry. It is exhibited in the miscellaneous class at dog shows sanctioned by the American Kennel Club. See dog.