Nicholas A. Christakis, MD, PhD, MPH, is a sociologist and physician who conducts research in the areas of social networks and bio-social science. He directs the Human Nature Lab. His current research is mainly focused on two topics: (1) the social, mathematical, and biological rules governing how social networks form (“connection”), and (2) the social and biological implications of how they operate to influence thoughts, feelings, and behaviors (“contagion”). His lab uses both observational and experimental methods to study these phenomena, exploiting techniques from sociology, computer science, bio-social science, demography, statistics, behavior genetics, evolutionary biology, epidemiology, and other fields. To the extent that diverse phenomena can spread within networks in intelligible ways, there are important policy implications since such spread can be exploited to improve the health or other desirable properties of groups (such as cooperation or innovation). Hence, current work in the lab involves conducting field experiments: some work involves the use of large-scale, online network experiments; other work involves large-scale randomized controlled trials in the developing world where networks are painstakingly mapped. Finally, some work in the lab examines the biological determinants and consequences of social interactions and related phenomena, with a particular emphasis on the genetic origins and evolutionary implications of social networks.