Substance abuse is the most common comorbid complication of severe mental illness. Current clinical research converges on several emerging principles of treatment that address the scope, pace, intensity, and structure of dual-diagnosis programs. They include a) assertive outreach to facilitate engagement and participation in substance abuse treatment, b) close monitoring to provide structure and social reinforcement, c) integrating substance abuse and mental health interventions in the same program, d) comprehensive, broad-based services to address other problems of adjustment, e) safe and protective living environments, f) flexibility of clinicians and programs, g) stage-wise treatment to ensure the appropriate timing of interventions, h) a longitudinal perspective that is congruent with the chronicity of dual disorders, and i) optimism.