Dement is one of our foremost sleep watchers--founder of the Sleep Laboratory at Stanford University and director of the university's Sleep Disorders Clinic. Next to sex, sleeping and dreaming may be one of the more irresistible topics of study. (About 500 students register for Dement""s basic course every year.) In this short volume, Dement summarizes the major theories and findings. Among the fascinations: we cycle through non-rapid eye movement (NREM) and rapid eye movement (REM) periods of sleep about six times a night. In REM sleep our bodies are virtually paralyzed but our eyes are active and we do most of our dreaming. Extraneous sensations can be incorporated in our dreams, and occasionally a dream can produce a solution to a problem. (Kekule's hexagonal structure of the benzene ring came to him in a dream in which he saw six snakes biting each others' tails as they whirled in a circle.) Enforced wakefulness may lead to psychotic symptoms in some, little bother in others. And so on. This is a fine example of popularization by an expert who clearly distinguishes between fact and speculation. Further, Dement includes carefully explained technical diagrams and provides a bibliography which is a model of explication.