The Epidemic Intelligence Service (EIS) was established in 1951 at the Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, as a combined training and service program in the practice of applied epidemiology. Since then, nearly 2,500 professionals have served in this 2-year program of the US Public Health Service. The experience of an EIS Officer has been modified because of the increased need for more sophisticated analytical methods and the use of microcomputers, as well as CDC's expanded mission into chronic diseases, environmental health, occupational health, and injury control. Officers who have entered the EIS in the past 20 years are more likely than their predecessors to stay in public health either at the federal level or in state and local health departments. The EIS Program continues to be a critical source for health professionals trained to respond to the demand for epidemiologic services both domestically and internationally.