In 2004 the United States Conference of Mayors, a nonpartisan organization of cities with populations higher than 30,000, surveyed the mayors of major cities on the extent and causes of urban homelessness, and most of the mayors named the lack of affordable housing as a cause of homelessness. (See Table 1.1.) The next three causes identified by mayors, in rank order, were mental illness or the lack of needed services (twenty-one of twenty-seven), substance abuse and lack of needed services (twenty), and low-paying jobs (sixteen). The lowest ranking cause, cited by five mayors, was prisoner reentry (release from incarceration). Other causes cited were unemployment (thirteen of twenty-seven), domestic violence (twelve), and poverty (seven).
As evident in the findings of the Conference of Mayors survey, homelessness is a complex social problem arising from three fundamental and interacting causes: lack of means, medical conditions, and behavioral problems.