A therapy dog is a dog that might be trained to provide affection and comfort to people in hospitals, retirement homes, nursing homes, schools, hospices, disaster areas, and to people with mental disorders, such as anxiety disorder or autism.
Therapy dogs are usually not assistance or service dogs, but can be one or both with some organizations.[1]
In the U.S., therapy dogs are not service animals and are not afforded the same privileges as service animals are.[2]

Therapy dog breeds are also useful for children who have autism and various learning disabilities.

A service dog is a type of assistance dog specifically trained to help people who have disabilities, such as visual impairment, hearing impairments, mental illnesses (such as posttraumatic stress disorder (PTSD)), seizure disorder, mobility impairment, and diabetes.
Desirable character traits in service animals typically include good temperament or psychological make-up (including biddability and trainability) and good health (including physical structure and stamina). Some service dogs are bred and trained by service dog organizations, while others are bred by breeders, and trained by private trainers or even the individuals with disabilities who will someday become their partners. Labrador Retrievers, Golden Retrievers, Labrador Retriever/Golden Retriever crossbred dogs, and German Shepherd Dogs are among the most common dog breeds working as service dogs today in the United States. Although dogs of almost any breed or mix of breeds may be capable of becoming a service dog, very few dogs have the requisite health and temperament qualities. Such a dog may be called a “service dog” or an “assistance dog”, the terminology typically varying by country or region.