Family-based therapy is one of the most thoroughly studied treatments for adolescent drug abuse. Considerable empirical support exists for the efficacy of family-based therapy in curtailing adolescent drug use and cooccurring behavior problems. This article extends knowledge of the effects of family-based therapy for adolescent drug abuse by reviewing 16 controlled trials and 4 therapy process studies from a treatment development perspective. We articulate knowns and unknowns regarding the outcomes of treatment as well as the components, processes, mechanisms, moderators, and boundaries of effective family-based therapy for adolescent drug abuse. The review highlights areas of progress and future research needs within the specialty of family-based therapy for adolescent drug abuse.