Homelessness in the US is a social problem of enormous public health significance. It was estimated in 2007 that 671,859 individuals were homeless, of which about two-thirds were single individuals and one-third were families; about 5 to 7.7% of young people, ages 15 to 24 years are homeless in the United States every year, making them more at risk for HIV, substance abuse, mental illness and victimization than adolescents in the general population (for updated New York City homelessness statistics, please click here). Given the current economic climate, many more individuals and families are expected to experience homelessness over the course of this year...