Walter Willett, MD, DrPH, has been the PI of the NHS II since its founding in 1989. He is Professor of Medicine at Harvard Medical School, and Chair of the Department of Nutrition and the Fredrick John Stare Professor of Epidemiology and Nutrition at the Harvard T.H. Chan School of Public Health. Dr. Willett’s research primarily involves the investigation of dietary factors, using epidemiologic approaches, in the cause and prevention of chronic disease. Fundamental to this work has been the development of methods to measure dietary intake in large populations.