Since the Nobel Prize for Physiology and Medicine was awarded to researchers of circadian rhythms in 2017, no serious biomedical researcher (and no responsible physician) can be excused for not being aware of the importance of the circadian organization of bodily processes. Now in its fourth edition, Circadian Physiology offers a thorough review of principles and applications of research on circadian rhythms and serves as a comprehensive introduction to the field for life scientists, as a valuable reference book for circadian researchers, as a primer for health practitioners, and as an all-inclusive textbook for university students. New in the fourth edition: every chapter updated with new research findings; 800 text figures now in full color; over 8,000 bibliographic sources now with DOIs.