Dr. Walter Willett is a physician and epidemiologist and Professor of Epidemiology and Nutrition at the Harvard T.H. Chan School of Public Health. He served as Chair of the Department of Nutrition at Harvard for 25 years. Much of his work has been on the development of methods, using both questionnaire and biochemical approaches, to study the effects of diet on the occurrence of major diseases. He has applied these methods starting in 1980 in the Nurses’ Health Studies I and II and the Health Professionals Follow-up Study. Together, these cohorts that include nearly 300,000 men and women with repeated dietary assessments are providing the most detailed information on the long-term health consequences of food choices. Dr. Willett has published over 2,000 research papers, primarily on lifestyle risk factors for heart disease and cancer, and has written the textbook, Nutritional Epidemiology, published by Oxford University Press. He also has four books for the general public. Dr. Willett is the most cited nutritional scientist internationally. He is a member of the National Academy of Medicine and the recipient of many national and international awards for his research.