This issue of the Emergency Medicine Clinics of North America focuses on the spectrum of public health issues that significantly impact the practice of emergency medicine and which are faced by practicing emergency physicians on daily basis. Topics include public health research in the emergency department; respiratory threats; emerging infectious diseases; emergency department overcrowding; end-of-life care; racial and ethnic disparities; issues of health promotion and disease prevention encompassing substance abuse, alcohol, and injury and violence; and public health surveillance; and the problems of homeless and disadvantaged patients. This article gives a brief introduction to the important relationship between emergency medicine and public health. (Authors)