The ADA defines a Service Animal as any Psychiatric Service Dog, Guide Dog, Signal Dog, or other animal individually trained to provide assistance to an individual with a disability, so long as the person’s disability falls under the ADA’s definition of physical or mental impairment or condition. An animal belonging to someone who is not disabled is not a Service Animal under the ADA.

Psychiatric Service Dogs perform some of the functions and tasks that the individual with a disability, including mental health instability, cannot perform for him or herself alone. Guide Dogs are one type of Service Animal that most people are familiar with; they are used by disabled individuals who are blind. But there are Service Animals that assist persons with other kinds of disabilities in their day-to-day activities. Some examples include: Alerting people with hearing impairments to sounds; pulling wheelchairs or carrying and picking up things for people with mobility impairments; assisting persons with mobility impairments with balance; assisting persons with mental impairments with tactile stimulation or buffering in crowded public places.

Under US law an Emotional Support Animal (ESA) is a pet which provides therapeutic benefit to its owner through companionship and affection. Emotional Support Animals are not required to have any specialized training, they require only as much training as an ordinary pet requires in order to live peacefully among humans without being a nuisance or a danger to others

There are two federal laws which grant special rights to owners of Emotional Support Animal:

The Fair Housing Amendments Act of 1988 (42 USC 3601, et seq.) allows you to live/stay anywhere you like without pet fees. Any home, any lodging-even ones that specifically prohibit Dogs. The Air Carrier Access Act allows you to travel on any airline without paying any pet fees and your Emotional Support Animal is allowed to accompany you in the cabin.

In the last 18 months, Airlines have become very strict and have introduced specific forms requiring medical professional references to prove the owner's need and entitlement for emotional support.  

Many people confuse the term Therapy Dog with Service Animal or Emotional Support Animal.  

Therapy Dogs and their Handlers have no Legal rights.  A Therapy Dog provides affection and comfort to people in hospitals, retirement homes, nursing homes, schools, people with learning difficulties, and stressful situations, such as disaster areas. Institutions may invite, limit, or prohibit access to therapy dogs. If allowed, these institutions will have their own requirements for Therapy Animals.

Therapy dogs are not Service Animals. A Service Animal has a skill which directly reduces the effect of a disability and so can legally accompany their disabled handler anywhere they can legally go.