Group psychotherapy or group therapy is a form of psychotherapy in which one or more therapists treat a small group of clients together as a group. The term can legitimately refer to any form of psychotherapy when delivered in a group format, including art therapy, cognitive behavioral therapy or interpersonal therapy, but it is usually applied to psychodynamic group therapy where the group context and group process is explicitly utilized as a mechanism of change by developing, exploring and examining interpersonal relationships within the group. The broader concept of group therapy can be taken to include any helping process that takes place in a group, including support groups, skills training groups (such as anger management, mindfulness, relaxation training or social skills training), and psychoeducation groups. The differences between psychodynamic groups, activity groups, support groups, problem-solving and psychoeducational groups have been discussed by psychiatrist Charles Montgomery. Other, more specialized forms of group therapy would include non-verbal expressive therapies such as art therapy, dance therapy, or music therapy. History The founders of group psychotherapy in the United States were Joseph H. Pratt, Trigant Burrow and Paul Schilder. All three of them were active and working at the East Coast in the first half of the 20th century. In 1932 Jacob L. Moreno presented his work on group psychotherapy to the American Psychiatric Association, and co-authored a monograph on the subject. After World War II, group psychotherapy was further developed by Moreno, Samuel Slavson, Hyman Spotnitz, Irvin Yalom, and Lou Ormont. Yalom's approach to group therapy has been very influential not only in the USA but across the world. An early development in group therapy was the T-group or training group (sometimes also referred to as sensitivity-training group, human relations training group or encounter group), a form of group psychotherapy where participants (typically, between eight and 15 people) learn about themselves (and about small group processes in general) through their interaction with each other. They use feedback, problem solving, and role play to gain insights into themselves, others, and groups. It was pioneered in the mid-1940s by Kurt Lewin and Carl Rogers and his colleagues as a method of learning about human behavior in what became the National Training Laboratories (also known as the NTL Institute) that was created by the Office of Naval Research and the National Education Association in Bethel, Maine, in 1947. Moreno developed a specific and highly structured form