This book is the first in a new series entitled ''Advances in Circadian Physiology." Our aim in this and subsequent volumes is to document and critically analyze the state of knowledge on biological clocks, circadian rhythms and their applications to human health, safety, performance and productivity. In the past twenty years, scientists have uncovered an elegant system of biological clocks in the brain that govern the daily rhythms of sleep and alertness, hormone levels and temperature and a myriad other aspects of body function. From the first identification of the suprachiasmatic biological clock in the early 1970s, this field of research has exploded in information and implication. These biological clocks, so perfectly attuned to the pace of a bygone era, are the root cause of the human fatigue, error, accidents and reduced productivity precipi tated by the around-the-clock challenges of today's industry and society. Research on these clocks offers the promise of fundamental solutions which can help the human race adjust physiologically to the technology-paced world we have created.