This collection reports on the latest research on an increasingly pivotal issue forevolutionary biology: cooperation. The chapters are written from a variety of disciplinaryperspectives and utilize research tools that range from empirical survey to conceptual modeling,reflecting the rich diversity of work in the field. They explore a wide taxonomic range,concentrating on bacteria, social insects, and, especially, humans. Part I ("Agents andEnvironments") investigates the connections of social cooperation in social organizations to theconditions that make cooperation profitable and stable, focusing on the interactions of agent,population, and environment. Part II ("Agents and Mechanisms") focuses on how proximate mechanismsemerge and operate in the evolutionary process and how they shape evolutionary trajectories.Throughout the book, certain themes emerge that demonstrate the ubiquity of questions regardingcooperation in evolutionary biology: the generation and division of the profits of cooperation;transitions in individuality; levels of selection, from gene to organism; and the "human cooperationexplosion" that makes our own social behavior particularly puzzling from an evolutionaryperspective.