PROJECT SUMMARY Adolescent depression is a prevalent and debilitating disorder that places youth at risk for suicidality, other psychiatric diagnoses, and functional impairment both during adolescence and into adulthood. There are a number of effective treatments; however, 30-50% of adolescents who receive these treatments do not respond. To improve response rates, practice parameters recommend routine systematic symptom assessment over the course of treatment to inform decisions regarding whether to switch or augment treatment. Research also demonstrates that regular symptom monitoring improves treatment outcomes. Unfortunately, routine symptom assessment in usual care for adolescent depression is extremely rare. In addition, for psychotherapy, which is the most frequent treatment for adolescent depression, there are currently no guidelines to direct therapists regarding how to use those symptom assessments to guide subsequent treatment decisions. Addressing this critical knowledge gap requires identifying (1) what symptoms or patient characteristics to assess, (2) when to administer those assessments, and (3) what subsequent treatment to provide, based on those assessments. Adaptive treatment strategies (ATSs) provide algorithms for guiding treatment decision making. These algorithms are based on patient characteristics and outcomes collected during the course of therapy, and they provide guidelines regarding when, how, and for whom midcourse changes in the treatment approach should be initiated. ATSs can be developed and validated within the context of an innovative experimental design called a sequential multiple assignment randomized trial (SMART). In a SMART, subjects can be randomized multiple times and these randomizations occur sequentially through time at selected critical decision points. The results of the SMART are used to define the decision rules that make up the ATS. The purpose of the current study is to evaluate the effectiveness of two ATSs for adolescent depression. The ATSs include delivery of an evidence-based psychotherapy for adolescent depression (interpersonal psychotherapy, IPT-A), systematic symptom monitoring, and an empirically-derived algorithm that specifies whether, when, and how to augment IPT-A. 200 depressed adolescents (age 12-18) will be recruited to participate in a 16-week SMART conducted in an outpatient community mental health clinic. The aims of this R01 are to (1) evaluate the effectiveness of the ATSs embedded in this trial, (2) evaluate adolescents' interpersonal functioning as a treatment target of IPT-A, (3) evaluate moderators of initial treatment and treatment augmentation strategies, and (4) conduct a process evaluation to identify barriers and facilitators that influenced ATS implementation.