Eighty million people from industrialized nations travel to the developing world each year. These travelers are ideally suited to effectively detect and monitor endemic and emerging infections of potential global impact at their points of entry into domestic populations and to track ongoing trends in travel-related morbidity. Travelers visit every country and expose themselves to diverse environments and pathogens. They often return home during or just after the incubation period to an advanced medical care system that can accurately diagnose known diseases and is poised to identify new pathogens or new variants. This chapter provides illustrative examples, including dengue, malaria, schistosomiasis, chikungunya, SARS, and avian influenza. © 2009 Blackwell Publishing.