In 1949, Alexander Langmuir became the first chief epidemiologist at the Communicable Disease Center (CDC) in Atlanta, Georgia. Among his many contributions to the agency and to public health, 2 of the most important--the Epidemic Intelligence Service (EIS) and his particular brand of epidemic-assistance investigation (the Epi-Aid)--are highlighted in this supplement to the American Journal of Epidemiology. What makes these and many other of Langmuir's innovations so remarkable is their continued relevance to the health challenges we face in this new century. CDC (now the Centers for Disease Control and Prevention) is recognized globally for its quality science, not only in epidemiology and laboratory practice but also in the behavioral and social sciences, statistics, and economics. Support to state and local health departments has been instrumental to CDC's success during its first 60 years, and the articles describing Epi-Aids in this supplement capture this partnership elegantly. They also reflect the evolution of CDC from an agency focused almost entirely on communicable diseases to one engaged in a broad array of global public health challenges.