Abstract
Rosbash discusses the circadian rhythms that regulate living organisms. These rhythms function on the much more familiar timescale of twenty-four hours. The name 'circadian' comes from the Latin circa dia and means 'about a day.' This is because circadian periods do not last exactly twenty-four hours but rather vary somewhat from organism to organism. These inexorable rhythms, due to the persistent beating of a biological clock in our brains and in other tissues, serve to coordinate many features of our behavior, metabolism, and physiology - even our sleep-wake cycle.