This article provides an overview of the role of the emergency department (ED) in the care of homeless and disadvantaged populations. It suggests that organized emergency medicine can have a significant impact on total community health by maintaining a universal "safety net" for the delivery of integrated health and human services. The epidemiology of social deprivation among ED patients is examined, with a particular focus on homelessness. Current research on the value of socio-medical integration in the ED setting is discussed, with emphasis on selected initiatives that have demonstrated feasibility, cost-effectiveness, and impact.