Animal-assisted therapy (AAT) has been shown to be effective in the treatment of many psychological disorders, including autism spectrum disorders, depression, anxiety, and posttraumatic stress disorder (PTSD). AAT can be used as an adjunct to other forms of psychotherapy. With AAT, the animal becomes a part of the treatment plan. Outcomes for clients that are associated with the use of AAT include (1) increased sense of comfort and safety, (2) increased motivation, (3) enhanced self-esteem, (4) increased prosocial behaviors, and (5) decreased behavioral problems. AAT provides a bridge for the therapist to develop a therapeutic relationship with a client, and the animal can provide supportive reassurance for the therapist. The amount of data that supports the benefits of AAT for the treatment of those with mental illnesses is growing, but evidence-based research that supports its use is lacking. Further research is needed.