Social science is the study of individuals, relationships, and institutions in human societies, past and present. Phenomena of interest include everything from the working of neurons in the brain to the behavior of socially situated individuals, from interactions within and among groups like families and communities as well as organizations and governments, to large-scale patterns of international trade, alliance, migration, and conflict. Social scientists engage vital normative questions—such as the relationship between freedom and morality, or the responsibilities of citizens in a democratic polity—by examining and debating classical and contemporary ideas in social thought and political philosophy, and they employ a wide variety of research methodologies, from laboratory studies and field experiments to interviews and ethnography, from surveys to the analysis of existing “big data” (e.g., from government or business records, social media or other online content).