Nicholas A. Christakis, MD, PhD, MPH, is an internist and social scientist who conducts research on social factors that affect health, health care, and longevity. He is a Professor of Medical Sociology in the Department of Health Care Policy at Harvard Medical School; Professor of Sociology in the Department of Sociology in the Harvard Faculty of Arts and Sciences; and an Attending Physician in the Department of Medicine at the Harvard-affiliated Mt. Auburn Hospital. Dr. Christakis received his BS from Yale University in 1984, his MD from Harvard Medical School and his MPH from the Harvard School of Public Health in 1989, and his PhD from the University of Pennsylvania in 1995. He was elected to the Institute of Medicine of the National Academy of Sciences in 2006. His current research focuses on health and social networks, and specifically with how ill health, disability, health behavior, health care, and death in one person can influence the same phenomena in others in a person's social network. This work involves the application of network science and mathematical models to understand the dynamics of health in longitudinally evolving networks. To the extent that health behaviors such as smoking, drinking, or unhealthy eating spread within networks in intelligible ways, there are substantial implications for public health and health policy. This body of work has also engaged the spread of obesity and of emotional states such as happiness, depression, and loneliness within social networks. Dr. Christakis' past work was focused on topics related to end-of-life care, such as hospice care, widowhood and caregiver burden, ICU decision-making, and the role of prognostication in medicine (about which he has written two books).