The study of moderation and mediation of youth treatment outcomes has been recognized as enormously beneficial in recent years. However, these benefits have never been fully documented or understood by researchers, clinicians, and students in training. After nearly 50 years of youth treatment outcome research, identifying moderators and mediators is the natural next step-shifting focus to mechanisms responsible for improved outcomes, identifying youth who will benefit from certain treatments or who are in need of alternative treatments, and recognizing the challenges associated with the study...