Neurology, by virtue of its study of the brain, is the primary medical science for the elucidation of the anatomy, physiology, pathology and, ultimately, the function of sleep. There has been nothing short of a revolution in the science of sleep over the past 50 years. From the discovery of REM sleep to the identification of Hypocretin/Orexin the basic science and clinical field of sleep medicine has blossomed. This article will explore the anatomy, physiology, biochemistry and, to a limited extent, pathophysiology of the sleep/wake centers of the brain. The field of chronobiology will also be touched upon.