Beginning on March 15, 2011, under Titles II and III of the ADA, the definition of a service animal is: "A service animal is a dog that is individually trained to do work or perform tasks directly related to the person’s disability." 

Examples of service animal tasks include:

--Guiding a person who is blind.

--Pulling a wheelchair.

--Alerting a person who has a seizure disorder.

--Providing physical support and assistance with balance and stability.

--Assisting persons with psychiatric and neurological disabilities by preventing or interrupting impulsive or destructive behaviors

--Providing a safety check or a room search for a person with Post Traumatic Stress Disorder (PTSD)

An animal that provides only emotional support, comfort, therapy, or crime prevention is not considered a service animal under the ADA. A service animal is a working animal; not a pet. Laws similar to the ADA, as well as local states; counties; and cities, may have different and more broad definitions of "service animal." Check with your local ADA Center.

For additional information, take a look at the following resources: 

Fact Sheet: Service Animals [2]

Service Animal Resource Hub [3]

Service Animal or Emotional Support Animal: What is the Difference? [4]