The homeless are amongst the most vulnerable groups in developed regions, suffering from high rates of poorly controlled chronic disease, smoking, respiratory conditions, and mental illness, all of which render them vulnerable to new and resurgent disease processes associated with climate change. To date, there have been no papers reviewing the impacts of climate change on the homeless population. This paper provides a framework for understanding the nature of such an impact. We review four pathways: increased heat waves, increased air pollution, increased severity of floods and storms, and the changing distribution of West Nile Virus. We emphasize the need for further debate and research in this field.