Research suggests that as many as 110,000 single adults with severe mental illness (SMI) are homeless on any given day in the United States. The combination of mental illness and homelessness make this population especially hard to reach through either housing or mental health programs alone. Supportive housing programs, which provide independent housing along with health and social services, hold great promise for this population, but are costly to launch and maintain. This Issue Brief highlights a landmark study that examines the extent to which supportive housing costs are offset by reductions in the use of public services for health, corrections, and shelter.