Since 1859 there has been a section of the American Medical Association, with various names and with varying emphases, devoted to meteorology, medical topography, epidemic diseases, hygiene, sanitary science, industrial medicine, public health, and preventive medicine. The history of the section reflects the changes resulting from the solution of old problems and the emergence of new ones. Important advances resulted from the indentification of parasites and vectors concerned in transmissible diseases, the discovery of methods of immunization, the recognition of deficiency diseases, and the development of chemotherapy. New problems arise from the pollution of air and water by an increasingly dense population, the increase in the average age of the population, the constant introduction of new chemicals and processes into industry, and the accumulating exposure to ionizing radiations. In view of the accomplishments of the past, it is stimulating to consider the problems that lie ahead.