Many chronically homeless people have a serious mental illness like schizophrenia and/or alcohol or drug addiction. Most chronically homeless individuals have been in treatment programs, sometimes on dozens of occasions. The federal government’s definition of chronic homelessness includes homeless individuals with a disabling condition (substance use disorder, serious mental illness, developmental disability, or chronic physical illness or disability) who have been homeless either 1) continuously for one whole year, or 2) four or more times in the past three years. Research reveals that between 10 to 20 percent of homeless single adults are chronically homeless. This translates into between 150,000 to 200,000 people who experience chronic homelessness. Permanent supportive housing—housing linked with supportive services—is an effective strategy for ending chronic homelessness and it is cost effective.