This book examines the issue of rational cooperation, especially cooperation between people with conflicting moral commitments. Can such cooperation—the choice made by a group and the decision by each member to contribute to that choice— be understood as guided by reason? Can the activity of reasoning itself take a cooperative form? The book is distinctive in offering an account of what people can accomplish by reasoning together, of the role of deliberation in democratic decision making, and of the negotiation of the proper use of concepts.