This part introduction presents an overview of the key concepts discussed in the subsequent chapters. The part discusses the knowledge accumulated on individual and group therapy with adults and apply some of it to child and adolescent group counseling. It describes the way as to reflect both the shared elements and the uniqueness of group work with different age groups. Child group psychotherapy was first suggested by S. R. Slavson and E. Redle, who labeled it activity group therapy, stressing the expression of feelings and fantasies through action, activities, and play. The literature on individual therapy with adults has suggested that integrative interventions are more appropriate than any single theory. The part argues that even the best single theory cannot explain group work. I. D. Yalom argued that it is acceptable to borrow from the literature on individual and group therapy with adults and apply it to children.