Drug and alcohol abuse by people with severe and persistent mental illness (SPMI) is one of the most signifi cant problems facing the public mental health system. Referred to variously as people with dual disorders or dual diagnosis, mentally ill chemical abusers, and individuals with co-occurring psychiatric and substance disorders, these patients pose major problems for themselves, their families, clinicians, and the mental health system. Lifetime prevalence of substance abuse was assessed at 48% for schizophrenia and 56% for bipolar disorder in the Epidemiological Catchment Area study (Regier et al., 1990), and estimates of current abuse for the SPMI population range as high as 65% (Mueser, Bennett, & Kushner, 1995). Rates of abuse are likely to be even higher among impoverished patients living in inner city areas where drug use is widespread. Substance use disorders (SUDs) in people with SPMI begins early in the course of illness, and has a profound impact on almost every area of the person’s functioning and clinical care. People with SPMI and SUDs show more severe symptoms of mental illness, more frequent hospitalizations, more frequent relapses, and a poorer course of illness than do those with a single diagnosis. Th ey also have higher rates of violence, suicide, and homelessness. Th ey manifest higher rates of incarceration, greater rates of service utilization and cost of health care, poorer treatment adherence, and treatment outcome. People with schizophrenia are now one of the highest risk groups for HIV, and there are ample data to indicate that substance use substantially increases the likelihood of unsafe sex practices (Carey, Carey, & Kalichman, 1997), the primary source of infection in this population. Women with schizophrenia and comorbid substance use disorders are at substantial risk of being raped and physically abused (Gearon, Kaltman, Brown, & Bellack, 2003). Substance use also impairs information processing, which is particularly problematic for people with schizophrenia, given the range of cognitive defi cits characterizing the disorder (Tracy, Josiassen, & Bellack, 1995).