Societies in transition are often faced with new settings and/or new diseases that require a response in order for the affected group to thrive or survive. A lack of effective response by a transitional population to a new pathogen can lead to the group's disintegration. In a broad selection of 19 essays by distinguished researchers, the epidemiology and health status of prehistoric, historical, and present day populations in transition are thoroughly explored. Different models--biomedical, ethnomedical, ecological, and politicoeconomic--are used to illustrate the effects of transition on the health of human populations throughout the world.