The term Homeless describes individuals who are unable to secure and maintain a permanent housing situation. This lack of housing can be due to a variety of factors including job loss, health problems, family and relationship issues, or other personal circumstances. Homelessness can also be a result of discrimination and abuse. While homelessness is a serious issue in the United States, some communities have successfully implemented programs to help those affected by this problem. These programs can vary from shelters to transitional housing and can serve people from all walks of life.

The definition of homelessness has evolved over time, and is often influenced by the political, social, and economic conditions at the time. A growing body of research on homelessness is establishing that it can be a complex and often interrelated set of issues.

In the 1870s, urbanization and industrialization led to a great increase in poverty and unemployment that contributed to the emergence of tramps who rode trains across America in search of work. The social reformer and muckraker Jacob Riis, in his later photojournalism work, documented their deplorable living conditions and helped raise awareness about the problem. In recent decades, major forces have changed the nature of homelessness in the United States, including gentrification, deinstitutionalization of mental hospitals, the AIDS epidemic, and budget cuts to community-based care and affordable housing in the 1980s.

Although many people have misconceptions about homelessness, a large percentage of homeless people are employed. Many are single men or women, but families with children also account for a significant proportion of the homeless population. Homeless families have different needs and experiences than other homeless populations, and the rate of homelessness among families is rising faster than among individuals.

While the majority of homeless people are male, more than one-third of them are female, and almost two-thirds of those are under the age of 24. In addition, a large number of homeless individuals are veterans. The causes of homelessness are very diverse and can include a variety of circumstances, including substance use disorders and mental illness, as well as inadequate wages and discrimination in the workplace.

Homeless individuals and families may live in a variety of situations, from tents in the street to shelters and single room occupancy hotels (SROs). A wide range of methodologies have been used to collect data on homelessness. While the sites of collection differ, and data are collected at various times throughout the year, research has established that a substantial proportion of the homeless population is unable to obtain and maintain a stable place of residence.

The vast majority of homeless individuals are single adults, but there is a growing body of literature on homeless families and other subpopulations. Many studies have also focused on specific types of homelessness, such as the homeless mentally ill and those in rural areas. There is a growing body of evidence that strategies such as housing first and housing assistance can reduce the duration and severity of homelessness.