This study examined the fidelity of attachment-based family therapy (ABFT) for depressed adolescents. Trained observers used the therapist behavior rating scale (3rd version) to code therapist behaviors in 45 sessions of ABFT and 45 sessions each from two empirically based treatments for adolescent substance abusers: multidimensional family therapy (MDFT) and cognitive-behavioral therapy (CBT). Results indicate that ABFT therapists employed essential ABFT interventions, such as focusing on vulnerable affect, highlighting attachment-related themes, and promoting adolescent-parent reattachment through in-session enactments. In accordance with the sequential nature of the treatment, these interventions were used more extensively during the early stage of treatment, when there is a greater focus on reattachment. ABFT was perfectly discriminable from CBT, with ABFT therapists using more restructuring and reattachment interventions and CBT therapists using more signature CBT interventions, such as cognitive monitoring and homework. ABFT was also discriminable from MDFT, with ABFT therapists placing a greater emphasis on reattachment. These results suggest that ABFT is a viable and differentiated treatment. Together with prior findings supporting its efficacy, ABFT should be considered a promising new approach for working with depressed adolescents and their families.