Dogs' tails come in many lengths from the long, plume-like tail of the Borzoi to the small, bobbed tail of the Rottweiler. Some dogs with bobbed tails are born that way. More often, however, they have their tails surgically docked a few days after birth. Docking refers to removal of part or all of a dog's tail. This usually is done at 1 to 3 days of age for cosmetic purposes, to retain the look that is characteristic of that breed. Occasionally, a dog must have his tail docked because of repeated injury.

The tail helps the dog maintain his balance, especially when jumping, turning at fast speeds, accelerating, and braking. The tail also is used as a rudder during swimming. The heavy tail of a Retriever can also help balance the weight of the game carried in his mouth.

Dogs use their tails in communication, both with other dogs and with humans, and the tail speaks volumes. A gently wagging tail expresses contentment and is a dog's equivalent of smiles and laughter. A stiffly wagging tail that swishes back and forth deliberately can indicate a threat. A tail held high can indicate confidence or aggression, and a tail held low or tucked between the legs signifies submission or anxiety.