Sleep is necessary for normal psychological functioning, and psychological function in turn affects sleep integrity. Recent investigations delineate the relation of sleep to a broad array of processes ranging from learning and memory to emotional reactivity and mood, and use a variety of methodological approaches (imaging, electrophysiological, behavioral) to reveal the complex relations between sleep and the functioning of the awake brain. The articles in this issue advance our fundamental knowledge of the relation of sleep to psychological function. In addition, several of the articles discuss how sleep is affected by or affects human clinical conditions, including insomnia, epilepsy, mild cognitive impairment, bipolar disorder, and cancer. Together, the articles of this special issue highlight recent progress in understanding the behavioral neuroscience of sleep and identify promising areas for future research, including the possibility of sleep-based interventions to improve psychological health.