This paper describes the development and implementation of the Boston Medical Center (BMC) Advanced Clinical Capacity for Engagement, Safety, and Services Project. In October 2002, the BMC Division of Psychiatry became the first such entity to open a Safe Haven shelter for people who are chronically homeless, struggling with severe mental illness, and actively substance abusing. The low-demand Safe Haven model targets the most difficult to reach population and serves as a "portal of entry" to the mental health and addiction service systems. In this paper, the process by which this blended funded, multi-level collaboration, consisting of a medical center, state, city, local, and community-based consumer organizations, was created and is maintained, as well as the clinical model of care is described. Lessons learned from creating the Safe Haven Shelter and the development and implementation of the consumer-informed evaluation are discussed as well as implications for future work with this population.