In order to better understand sleep initiation and maintenance disorders research into human chronobiology is necessary. Some patients suffering from insomnia seem to show abnormal circadian rhythms of core body temperature and melatonin onset. These circadian rhythm angles are associated with difficulties falling asleep and with complaints of early morning awakenings. Chronobiological treatments aim to enhance appropriately timed input to the circadian timing system to support its role in sleep regulation. Nevertheless, the evidence of their effects remains unclear in patients with insomnia. Moreover, future research should examine the effects of cognitive behavioral therapy for insomnia on circadian factors.