Ending housing instability and homelessness is critical for improving public health and community well-being. Studies show much higher rates of physical health issues and mental health and/or substance use disorders among populations experiencing homelessness than among people who are stably housed. People experiencing homelessness often face a decline in their physical and mental health while sheltered or unsheltered; therefore, this is an important window for initiating mental health and/or substance use disorder treatments. This guide provides strategies and implementation considerations for behavioral health providers and others practitioners to: 
• Engage people currently experiencing homelessness
• Build strong relationships with these individuals
• Offer effective mental health and/or substance use disorder treatments
• Improve retention in recovery efforts
The guide includes four case studies to highlight strategies for providing treatment and recovery support services to people experiencing both unsheltered and sheltered homelessness. Additionally, it presents considerations for evaluation and quality improvement