OBJECTIVE: Clinical services for psychiatrically impaired populations have only recently been studied with scientifically valid designs to explore innovations in structure, accessibility, and financing. Health systems reform in the United States has provided the impetus for better defining clinically effective and cost-sensitive models for mental health services. This article reviews assertive community treatment, used for adults with severe mental illnesses, and multisystemic therapy, used for adolescents with serious emotional disturbances, as examples of service system innovations that have been studied with controlled clinical trial designs and have demonstrated efficacy in treating difficult and costly clinical populations. METHOD: The authors reviewed the published controlled clinical trials of assertive community treatment and multisystemic therapy, focusing on the clinical and administrative elements that distinguish them from traditional service systems. RESULTS: A qualitative assessment of these two approaches suggests that they share common elements, with important implications for mental health policy. Specifically, the use of an ecological model of behavior applied to mental health patients is critical to both systems. In addition, therapeutic principles emphasizing pragmatic (outcome-oriented) treatment approaches, home- based interventions, and individualized goals are key elements of their success. Most important, both systems embody a therapeutic philosophy demanding therapist accountability, in which personnel are rewarded for clinical outcomes and therapeutic innovation rather than for following a prescribed plan. CONCLUSIONS: As empirically tested approaches, assertive community treatment and multisystemic therapy provide a scientific foundation for continued reform and serve to illustrate critical elements in designing new community treatment initiatives for behavioral as well as medical conditions.Abstract Teaser