Ichiro Kawachi, M. D, Ph. D, is Professor of Health and Social Behavior, and the Director of the Harvard Center for Society and Health, both at the Harvard School of Public Health. Dr Kawachi's research has focused on uncovering the social and economic determinants of population health. He is the co-Edtor (with Lisa Berkman) of Social Epidemiology, published by Oxford University Press in 2000, as well as co-author of The Health of Nations, with Bruce Kennedy (The New Press, 2002). He is a member of the Research Advisory Committee of the Pan-American Health Organization/WHO. Dr Kawachi serves as the Senior Editor (for social epidemiology) of the journal Social Science and Medicine, as well as an Editor of the American journal of Epidemiology. Lisa E Berkman, Ph.D., is Thomas D. Cabot Professor of Public Policy and Epidemiology and Chair of the Department of Health and Social Behavior at the Harvard School of Public Health. Dr Berkman is a social epidemiologist whose research examines inequalities of health linked to social isolation, socioeconomic status, race, and ethnicity. She is past president of the Society for Epidemiologic Research and a member of the Institute of Medicine. Dr Berkman coedited the first textbook in her field, Social Epidemiology, and wrote with Lester Breslow Health and Ways of Living, a seminal book about the major results of the Alameda County Study.