Mammalian hibernation is commonly thought of as something completely out of the ordinary, a "unique and unorthodox state." The present book takes the opposite view. It argues that the physiological achievements of hibernators do not deEend on special mechanisms but on special use of ordinary mechanisms. It is precisely this that makes the hibernators important. If the hibernators de pend on some unique physiological principle their study is that of a biological curio. But if they are using basic mammalian systems in a quantitatively extreme way, then they are a naturally occurring preparation of enormous potential. Hibernation involves every aspect of the animal's biology from fat metabo lism to behavior, from thermoregulation to dental caries; every system in the body is affected in some way or other by hibernation. A comprehensive account of hibernation would be almost coextensive with an account of the whole of mammalian biology. The present book does not attempt to describe everything that has been discovered about hibernation. Excellent coverage for that already exists in the proceedings of three recent symposia and in the other major source materials listed on page 233. There is in fact an enormous amount of information already available. But there is a difference between information and understanding. Despite the increasing volume of research and growing interest in mammalian hibernation, there is little appreciation of the essential characteristics of the phenomena. The pieces of the puzzle lie scattered.