Every so often there appears a work of synthesis which is so original and creative that it clarifies and systematizes a whole field of observation or knowledge that had hitherto been adventitious and chaotic. Such were the works of Rudolf Virchow, whose Cellular-Pathologie (1858) not only founded the science of pathology, but constituted the fundamental contribution to the rise of modern medicine, as was also Claude Bernard's Introduction à l'étude de la Médecine Experimentale (1865), which put physiology on a firm scientific basis as well as the founding of regulatory biology and its relation to human health. What these books, each in its own way, did for the growth and development of medicine and human health, I am convinced that Mrs Power's admirable book will do for the growth and development of our better understanding of the dynamics of social life not only among chimpanzees, but for all primates, including humans. For what the author has done is to make a microscopic examination of the fieldwork of numerous independent investigators who have studied chimpanzees under natural or artificial conditions. With great acumen she has seen that even under natural conditions, the conditions may not be as ‘natural’ as most investigators and their interpreters and readers may have thought, and that various factors under such conditions have led to a variety of inferences which have in fact been erroneous. Mrs Power's analysis of these factors for the first time really makes it possible to train future students of animal behavior, and more particularly of primate behavior, including humans, in the delicate methodology of fieldwork.