Chronically homeless individuals are those who spend long periods of time living on the street or other places not meant for human habitation, and who have one or more disabilities, frequently including mental illnesses and substance use disorders. In the 2014 Department of Housing and Urban Development (HUD) pointintime count of people experiencing homelessness, more than 84,000 individuals met the definition of chronically homeless, down from more than 120,000 in 2008. In part the decline is due to the federal government's plan, announced in 2002, to end chronic homelessness within 10 years. The target date has since been extended to 2017. Among the federal programs focused on ending chronic homelessness are the HUD Homelessness Assistance Grants, the HUD and Veterans Affairs Supported Housing Program (HUDVASH), and several HUD demonstration programs. One of the reasons that federal programs have devoted resources to ending chronic homelessness is studies finding that individuals who experience it, particularly those with serious mental illness, use many expensive services often paid through public sources, including emergency room visits, inpatient hospitalizations, and law enforcement and jail time. Even emergency shelter resources can be costly. In addition to potential ethical reasons for ending chronic homelessness, doing so could reduce costs in providing assistance to this population. This book summarizes the research surrounding permanent supportive housing (PSH) for chronically homeless individuals. In doing so, it attempts to examine the nuance in the research to determine where PSH could be considered successful and where gaps may remain. The book discusses what it means to be chronically homeless, the way in which assistance for chronically homeless individuals has evolved, and how federal programs target assistance to individuals experiencing chronic homelessness. In addition, it summarizes the research regarding chronically homeless individuals who move into PSH.