A service dog is a type of assistance dog, specifically trained to help people who have disabilities other than visual or hearing impairment. Desirable character traits include good temperament or psychological make-up, good health including physical structure, biddability and trainability. Service dogs are sometimes trained and bred by service dog organizations.

Some dogs are donated by private breeders, and some are selected from shelters. Any breed or mixture of breeds of dog might produce a representative capable of service work, though few dogs have all of the qualities in health, temperament, biddability, trainability and physical ability needed.

Such a dog may be called a "service dog" or an "assistance dog," depending largely on country. Other common names include "helper dog," "aide dog," and "support dog."