Like almost all light-sensitive living beings, human beings follow biological rhythms set on a period of about 24 hours. The circadian clock therefore describes the internal system that allows us to anticipate the changes of day and night by regulating nearly all the aspects of our physiology and behavior. At a time when our biological rhythms are increasingly undermined – whether by night work, jetlag, or societal habits, – scientists begin to unveil the impact such circadian misalignments may have in the explosion of metabolic diseases.