The whippet is a British breed of medium-sized dog, of the sighthound type, related to the larger greyhound and the smaller Italian greyhound. Apart from the differences in height, the whippet closely resembles these two breeds; it has sometimes been described as "the poor man's greyhound". It is kept as a companion dog, for competitive showing, for amateur racing as well as lure coursing. It has the highest running-speed of any breed in its weight and size range, and may have the fastest idle-to-running acceleration of any dog.

Sighthounds are a type of hound dog that hunts primarily by sight and speed, unlike scent hounds, which rely on scent and endurance.