In this book we trace the development of several major themes in sleep research, from the first formal description of REM sleep in the early 1950s through the present. Chapter 1 provides those less familiar with this area with a perspective on the many possible ways to examine sleep. Chapter 2 describes in detail a major viewpoint of this book: that observations of pharmacological interventions affecting the neurotrans­ mitters may aid in the understanding of sleep regulation. The remain­ der of the book is devoted to endocrine systems related to sleep (chap. 3) and to the contribution of sleep research to the understanding of various pathological states (chaps. 4-7). The areas of investigation open to those who wish to understand sleep are much broader than the traditional problems of insomnia and narcolepsy. Such disorders as depression, schizophrenia, and alcoholism have long been associated with disordered sleep. Our search for an understanding of the latter phenomena may clarify the nature of these conditions.