Human beings choose their friends, and often their neighbors and co-workers, and we inherit our relatives; and each of the people to whom we are connected also does the same, such that, in the end, we humans assemble ourselves into large face-to-face social networks—which we have recently taken online as well. How and why do we do this? And how might an understanding of human social network structure and function be used to intervene in the world? During this session, Dr. Nicholas Christakis will review recent research from his lab describing two classes of interventions—involving both offline and online networks—that can help make the world better: (1) interventions that rewire the connections between people, and (2) interventions that manipulate social contagion. Social contagion interventions modify the flow of desirable or undesirable phenomena between people, ranging from obesity to smoking cessation to altruism to pathogens to medication choice. Dr. Christakis will illustrate what can be done using a variety of experiments in settings as diverse as fostering health behavior change in developing world villages, fostering cooperation in networked groups online, facilitating the diffusion of innovation or coordination in groups, and other examples. By taking account of people's structural embeddedness in social networks, and by understanding social influence, it is possible to intervene in social systems to enhance desirable population-level properties as diverse as health, wealth, cooperation, coordination, and learning.