The founders of group psychotherapy in the USA 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.

After World War II, group psychotherapy was further developed by Jacob L. 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 the T-group or training group (sometimes also referred to as sensitivity-training group, human relations training group or encounter group) is a form of group psychotherapy where participants themselves (typically, between eight and 15 people) learn about themselves (and about small group processes in general) through their interaction with each other.