Circadian rhythm sleep disorders are a group of disorders in which the individual's sleep is misaligned with the normal sleep and wake times. This is due to lack of synchrony between the body circadian clock timekeeping mechanism and the 24-hour day-night cycle. Some of the disorders such as delayed sleep phase disorder, advanced sleep phase disorder, free running disorder, and irregular sleep wake rhythm disorder are due to abnormalities in the circadian clock timekeeping mechanism. There are other disorders such as shift work disorder and jet lag disorder in which the circadian clock timekeeping mechanism is normal but the problems arise due to mismatch caused by extrinsic factors (night or early morning shift work and air travel across multiple time zones). Proper recognition and treatment of these disorders are necessary to ameliorate the symptoms and minimize the adverse social and occupational impact.