The Treatment for Adolescents With Depression Study (TADS) was designed to compare the relative and combined effectiveness of cognitive behavior therapy (CBT) and fluoxetine, each of which had demonstrated efficacy in carefully controlled single-site studies. Models of CBT from these efficacy studies served as the foundation for the TADS psychosocial intervention. When interpreting the acute and long-term outcomes of TADS treatment in the context of other studies of CBT for major depression, it is critical to understand the process and the decision making that formed the TADS CBT intervention. The TADS CBT Committee reviewed meta-analyses of child and adolescent psychotherapy as well as studies of CBT for childhood and adolescent depression, relied on expert consultants, and evaluated the treatment process in a feasibility study to derive the essential components of TADS CBT. In this article we describe the rationale for the TADS CBT, the process of treatment design, and the immediate sources of the TADS treatment. Key decisions were made involving the degree of treatment structure, therapist flexibility versus cross-site consistency, duration and intensity of treatment, the involvement of family members in treatment, and core versus optional elements of the intervention.