The last four decades have witnessed considerable advances in our knowledge of the pharmacology of sleep. Both basic and clinical pharmacology have made major contributions toward our current understanding of the complex mechanisms of sleep and wakefulness. In addition, these advances in our understanding of the pharmacology of sleep have benefited the treatment of sleep disorders and various neurologic and psychiatric conditions. This volume is organized into three different parts. The first is a review of the basic mechanisms of sleep and wakefulness and the chronobiology of sleep. The second part reviews the basic pharmacology of the various neuro­ transmitter systems involved in sleep and wakefulness, while the third is clinically oriented and focuses on the effects of a variety of drugs on sleep and wakefulness. The initial part begins with a historical review of the hypotheses of the mechanisms of sleep, evolving from passive to active regulation, and concepts involving sleep-related neurotransmitters and other sleep factors. Then regulation of sleep and wakefulness is discussed in terms of homeostatic, circadian, and ultradian processes. Also discussed is the fact that sleep homeostasis is not disrupted by the administration of hypnotic drugs. This part also reviews time-dependent properties of pharmacologic agents in relation to endogenous biologic rhythms and more specifically to chrono­ pharmacologic changes.