The sleep-wake regulatory system and the circadian rhythm generating system are two brain networks integrated in the classical two-process model. These processes interact continuously, and to obtain an optimal sleep they must be correctly aligned. The suprachiasmatic nucleus located in the hypothalamus is crucial in the regulation of circadian rhythms, and the hypothalamus is a key component of the sleep-wake regulatory system in association with the thalamus, basal forebrain and brainstem. Alterations of these processes can result in a variety of sleep disturbances or sleep disorders.