This guide was written to assure that individuals with substance use disorders and co-occurring impairments that meet Social Security disability criteria receive Federal disability assistance under the Supplemental Security Income (SSI) program or the Social Security Disability Insurance (SSDI) program. The guide focuses on the complex issues involved in documenting impairments that co-occur with substance use disorders — particularly for homeless SSI/SSDI applicants, who are more likely than those with stable housing to be denied benefits for procedural rather than medical reasons. The information contained in this document is primarily intended for licensed physicians, psychologists, and other medical professionals who are authorized by the Social Security Administration (SSA) to provide medical evidence of impairment and for other clinicians (including nurses, physician assistants, and licensed clinical social workers) who assist with the documentation of medical and functional impairments in support of SSI/SSDI applications. For an explanation of SSI/SSDI eligibility criteria, how these programs differ, and the disability determination process, readers are referred to Documenting Disability: Simple Strategies for Medical Providers (O’Connell, Quick, and Zevin 2004). This document and other disability resources are available via the National Health Care for the Homeless Council’s website at http://www.nhchc.org/disabilityresources.html. 1 (Author)