This report presents the findings from an exploratory study of the Housing First approach of providing permanent supportive housing to single, homeless adults with mental illness and co-occurring substance-related disorders. In recent years, Congress and the leadership of the U.S. Department of Housing and Urban Development (HUD) have encouraged the development of permanent housing for homeless people. Concurrently, there has been a shift toward committing a greater proportion of HUD McKinney-Vento Act funds toward housing as opposed to supportive services and an increase in attention toward the hardest-to-serve, chronically homeless population, a substantial number of whom are mentally ill. Because it addresses this population and its needs, the Housing First approach is currently experiencing increased attention as a method of serving this population consistent with the above-stated goals.