Book excerpt: During the past decade many review papers and books have been devoted to descriptions and analyses of biological rhythms (chronobiology) in plants and animals. These contributed greatly to demonstrating the impor tance of bioperiodicities in living beings in general. However, the practi cal aspects of chronobiology with regard to human health and improving the treatment of disease have not yet been a major focus of publication. One of our aims is to establish the relevance of biological rhythms to the practice of medicine. Another is to organize and convey in a simple fashion information pertinent to health- and life-science professionals so that students, researchers, and practitioners can achieve a clear and pre cise understanding of chronobiology. We have limited scientific jargon to unavoidable basic and well-defined terms and we have emphasized illus trative examples of facts and concepts rather than theories or hypotheti cal mechanisms. This volume is divided into seven chapters, each of which is compre hensive in its treatment and includes an extensive bibliography. The book is organized to serve as a textbook and/or reference handbook of modem applied chronobiology. Chapter 1 describes the historical development of chronobiology and reviews why, when, and how major concepts were introduced, accepted, and transformed.