The terrier is a group of dog breeds initially bred for hunting and killing vermin. While usually small, these dogs are brave and tough with a lively, energetic, and almost hyperactive personality. The largest breed in this family is the Airedale Terrier.

Most terrier breeds were developed in the British Isles. They were used to control rats, rabbits, and foxes both over and under the ground. Some larger terriers were also used to hunt badgers. In fact, the word terrier comes from the Middle French terrier, derived from the Latin terra, meaning earth. The Kerry Blue Terrier and Airedale, however, are particularly noted for tackling river rats and otter in deep water.

The gameness of terriers was exploited by using them in so-called sporting contests. Initially, terriers competed in events such as clearing a pit of rats. The dog that was fastest in killing all the rats won. Bull Terriers, in particular, were developed as fighting dogs.