Group living is a widespread phenomenon amongst animals and has attracted considerable attention in a number of different contexts. This book focuses on the unifying concepts regarding group behaviour that have been developed over the last two decades. The authors discuss the mechanisms that govern the evolution and maintenance of grouping behaviour throughout the animal kingdom, and the factors that control observed group size and group composition in particular situations. Although the book's emphasis is on the elaboration of a conceptual framework, extensive examples and case studies illustrate the diversity of grouping phenomena across taxonomic boundaries, and demonstrate the general applicability of the concepts involved. Living in Groups will familiarize the reader with the latest ideas on the ecology and evolution of group-living animals, providing a summary and critical synthesis of the extensive and diverse literature on the subject.