In this book, prominent authors from disciplines as diverse as biology, philosophy, and the social sciences have assembled to consider the nature of cooperation and prosocial behavior at levels of social complexity ranging from the individual to the international. Successive sections cover key topics such as the relations between cooperation in animals and humans, the development of prosocial propensities in humans, aspects of the situation and of personality that increase the probability that individuals will behave prosocially, the relationships among trust, cooperation, and commitment, and cooperation between groups and nations. Three case studies that illustrate the important issue of international cooperation are also included. The chapters are integrated by a series of useful editorials that emphasize that a full understanding of cooperation and prosocial behavior requires us to move among different levels of social complexity.