From the family to the workplace to the marketplace, every facet of our lives is shaped by cooperative interactions. Yet everywhere we look, we are confronted by proof of how difficult cooperation can be—snarled traffic, polarized politics, overexploited resources, social problems that go ignored. The benefits to oneself of a free ride on the efforts of others mean that collective goals often are not met. But compared to most other species, people actually cooperate a great deal. Why is this? brings together insights from evolutionary biology, political science, economics, anthropology, and other fields to explain how the interactions between our evolved selves and the institutional structures we have created make cooperation possible. The book begins with a look at the ideas of Mancur Olson and George Williams, who shifted the question of why cooperation happens from an emphasis on group benefits to individual costs. It then explores how these ideas have influenced our thinking about cooperation, coordination, and collective action. The book persuasively argues that cooperation and its failures are best explained by evolutionary and social theories working together. Selection sometimes favors cooperative tendencies, while institutions, norms, and incentives encourage and make possible actual cooperation. will inspire researchers from different disciplines and intellectual traditions to share ideas and advance our understanding of cooperative behavior in a world that is more complex than ever before.