Dr. John Glasser studied biology at Princeton, population biology at Duke, and population sciences, international health, epidemiology and biostatistics at Harvard. After serving as an Epidemic Intelligence Service officer in the CDC’s Division of Reproductive Health, he returned to Harvard for a post-doctoral fellowship in mathematical biology with Richard Levins. Because modeling permits one to compare scenarios differing solely in interventions of interest, realistic mathematical modeling is among the most reliable means of evaluating public health programs. Such evaluations can be prospective, involving hypothetical interventions being contemplated, or retrospective, involving alternatives to ongoing programs. Since resuming my CDC duties, he has assisted in designing, or evaluating and occasionally improving public health programs at home and abroad by modeling transmission of the pathogens causing chlamydia, herpes simplex 2, AIDS, influenza, measles, pertussis, rotavirus, rubella and congenital rubella syndrome, SARS, smallpox, and both chickenpox and shingles, together with various mitigation strategies. He helped to formulate the US response were Variola major reintroduced by terrorists, to explain why earlier care-seeking for symptoms that might herald SARS, together with increasingly accurate diagnoses and effective isolation, had far more impact than quarantine, and to develop the gradient as a means of guiding vaccination programs in heterogeneous host populations whose members may mix non-randomly. The CDCs in China, Beijing and Taiwan, the Ministries of Health in Bolivia, Costa Rica, the states of S?o Paulo, Brazil, and Morelos, Mexico, the Romanian Public Health Institute, Swedish Institute for Communicable Disease Control, and World Health Organization have consulted him.