Wade Hampton Frost was the first professor of epidemiology at Johns Hopkins University, in the first department of epidemiology in the United States. He began his remarkable career with the US Public Health Service, where his greatest contributions included the recognition that mild and asymptomatic childhood polio produced lifelong immunity, and the development of methods for tracking influenza epidemics. From 1919, as a professor at the School of Hygiene and Public Health at John Hopkins, he trained many future leaders of American public health programs. He also made substantial contributions to epidemiologic methodology, including developing the concept of an index case during investigations of tuberculosis in Tennessee, the use of life-table methods for estimating secondary attack rates, the use of age cohorts for longitudinal studies, and-in collaboration with Lowell Reed-the first mathematical expression of the epidemic curve. Drawing on personal papers, recorded interviews, and archival material, Thomas M. Daniel recounts the story of Frost's life and work, and elucidates his seminal contributions to epidemiology and public health. George Comstock, Emeritus Centennial Alumni Professor of Epidemiology at Johns Hopkins has provided an introduction. Thomas M. Daniel is Professor Emeritus of Medicine and International Health and Emeritus Director of the Center for International Health at Case Western Reserve University.