An emotional support animal (ESA) is an animal that provides support to individuals with a mental health or psychiatric disability. Emotional support animals are not required to be trained. Any animal that provides support, comfort, or aid, to an individual through companionship, unconditional positive regard, and affection may be regarded as an emotional support animal.

In the United States, emotional support animals are not recognized as service animals under the Americans with Disabilities Act. Service animals are trained to perform specific tasks such as helping a blind person navigate. People with mental health disabilities who possess an emotional support animal may be exempt from certain federal housing and travel rules. To receive these exemptions, the handler must meet the federal definition of disabled, and the emotional support animal must help alleviate the symptoms or effects of the disability. The individual may need to present a letter from a certified healthcare provider, stating that the emotional support animal is needed for their mental health.

Emotional support animals are typically household domesticated animals, but may also be members of other animal species. There is no requirement under US federal law that an emotional support animal wear any identifying tag, patch, harness, or other indication that it is an emotional support animal.

There are no training requirements for emotional support animals, which typically have no training beyond what would be expected for the same type of animal. There is no requirement that they be individually trained to do work or perform tasks.

Although most companion animals are pets as opposed to emotional support animals, research studies document a correlation between companion animals and the improvement of their owners' mental health.

In 2020, the Assistance Dog Center, an assistance dog training service, and CertaPet, a company that connects potential clients with providers of animal-assisted therapy, announced the result of an online international survey of the owners of emotional assistance animals, obtaining responses from 298 people in relation to 307 ESA dogs. All participants reported that their quality of life had improved as a result of having an ESA dog, and almost all reported that having an ESA dog increased their feelings of security, independence, and energy, and helped improve their sleep.

A 2020 study, conducted in the UK through an online survey of almost 6,000 people, similarly found that almost 90% of people who had at least one companion animal during the COVID-19 pandemic described their animals as a source of considerable support, with that result being unaffected by the species of companion animal. The authors concluded that having a companion animal seemed to mitigate some of the negative psychological effects of the COVID-19 lockdown. Poorer mental health before the lockdown was associated with a stronger reported human-animal bond, and animal ownership was associated with smaller reported decreases in mental health and smaller increases in loneliness.

A 2018 review of 17 studies relating to companion animal ownership found that pets provide benefits to those with mental health conditions and that pets can be a source of calming support and companionship, as well as providing distraction and disruption from upsetting symptoms and experiences, and helping their owners maintain a positive identity and sense of self. The review found potential negative aspects of pet ownership, such as the significant distress associated with the loss of a pet. The authors recommended further rigorous research to test the apparent positive relationship between ownership of a companion animal and mental health.