A circadian rhythm is an endogenously driven roughly 24-hour cycle in biochemical, physiological or behavioural processes. Circadian rhythms have been widely observed, in plants, animals, fungi and cyanobacteria. This book presents current research from across the globe in the study of the biology, cognition and disorders associated with circadian rhythms. Topics discussed include circadian clocks and eating disorders; disruption of circadian rhythms in hypersomnia, insomnia and sleep movement disorders; circadian pacemaker in ovary and uterus during cell differentiation and apoptosis and emerging functions of heme in transcription associated with circadian rhythms.