Homelessness has always existed in the United States, but only in recent decades has the issue come to prominence.
In the 1970s and 1980s, the number of homeless persons increased, as did their visibility.
Experts cite various causes for the increase in homelessness. These include the demolition of single room occupancy dwellings in so-called “skid rows” where transient single men lived, the decreased availability of affordable housing generally, the reduced need for seasonal unskilled labor, the reduced likelihood that relatives will accommodate homeless family members, the decreased value of public benefits, and changed admissions standards at mental hospitals.
The increased visibility of homeless persons was due, in part, to the decriminalization of actions such as public drunkenness, loitering, and vagrancy.
Homelessness occurs among families with children and single individuals, in rural communities as well as large urban cities, and for varying periods of time. Depending on circumstances, periods of homelessness may vary from days to years.
Researchers have created three categories of homelessness based on the amount of time that individuals are homeless.
First, transitionally homeless people are those who have one short stay in a homeless shelter before returning to permanent housing.
In the second category, those who are episodically homeless frequently move in and out of homelessness but do not remain homeless for long periods of time.
Third, chronically homeless individuals are those who are homeless continuously for a period of one year or have at least four episodes of homelessness in three years. Chronically homeless individuals often suffer from mental illness and/or substance use disorders.
 Peter H. Rossi, Down and Out in America: The Origins of Homelessness (Chicago: The University of Chicago Press, 1989), 181-194, 41. See, also, Martha Burt, Over the Edge: The Growth of Homelessness in the 1980s (New York: Russell Sage Foundation, 1992), 31-126.
Down and Out in America, p. 34; Over the Edge, p. 123.
 See Randall Kuhn and Dennis P. Culhane, “Applying Cluster Analysis to Test a Typology of Homelessness by Pattern of Shelter Utilization: Results from the Analysis of Administrative Data,” American Journal of CommunityPsychology 26, no. 2 (April 1998): 210-212.