Service animals are defined as dogs that are individually trained to do work or perform tasks for people with disabilities. Examples of such work or tasks include guiding people who are blind, alerting people who are deaf, pulling a wheelchair, alerting and protecting a person who is having a seizure, reminding a person with mental illness to take prescribed medications, calming a person with Post Traumatic Stress Disorder (PTSD) during an anxiety attack, or performing other duties. Service animals are working animals, not pets. The work or task a dog has been trained to provide must be directly related to the person’s disability. Dogs whose sole function is to provide comfort or emotional support do not qualify as service animals under the ADA.

The Department of Justice has allowed for Service Dogs to be trained by their Handlers, thus fulfilling two separate and very important points. First, the cost of having a professional agency train a single Service Dog is, for many people with disabilities, a price that their budget can simply not handle. Secondly, it is recommended that Psychiatric Service Dogs are paired with, and trained by their handler, since each person's needs are unique.

Here is how the Department of Justice explains their decision:

Training requirement. Certain commenters recommended the adoption of formal training requirements for service animals. The Department has rejected this approach and will not impose any type of formal training requirements or certification process, but will continue to require that service animals be individually trained to do work or perform tasks for the benefit of an individual with a disability. While some groups have urged the Department to modify this position, the Department has determined that such a modification would not serve the full array of individuals with disabilities who use service animals, since individuals with disabilities may be capable of training, and some have trained, their service animal to perform tasks or do work to accommodate their disability. A training and certification requirement would increase the expense of acquiring a service animal and might limit access to service animals for individuals with limited financial resources.

Some commenters proposed specific behavior or training standards for service animals, arguing that without such standards, the public has no way to differentiate between untrained pets and service animals. Many of the suggested behavior or training standards were lengthy and detailed. The Department believes that this rule addresses service animal behavior sufficiently by including provisions that address the obligations of the service animal user and the circumstances under which a service animal may be excluded, such as the requirements that an animal be housebroken and under the control of its handler. “

You can read more about the Department of Justice and the Americans with Disabilities Act here:

http://www.ada.gov/service_animals_2010.htm