Focusing on the physiological and behavioral factors that enable a species to live in a harsh seasonal environment, this book places the social biology of marmots in an environmental context. It draws on the results of a forty-year empirical study of the population biology of the yellow-bellied marmot near the Rocky Mountain Biological Laboratory in the Upper East River Valley in Colorado, USA. The text examines life-history features such as body-size, habitat use, environmental physiology, social dynamics, and kinship. Considerable new data analyses are integrated with material published over a fifty-year period, including extensive natural history observations, providing an essential foundation for integrating social and population processes. Finally, the results of research into the yellow-bellied marmot are related to major ecological and evolutionary theories, especially inclusive fitness and population regulation, making this a valuable resource for students and researchers in animal behavior, behavioral ecology, evolutionary biology, ecology and conservation.