Circadian rhythms influence virtually every aspect of behavior. This special issue provides updates on the current state and future directions for the field of circadian rhythms in behavioral neuroscience. Recent data have linked circadian rhythms to behavioral and physiological phenomena and disease states in virtually every area of behavioral and biomedical science. Specifically, a growing interest in the cognitive, neuropsychiatric, and metabolic consequences of circadian rhythm disorders and dysfunction is emerging. This special issue is not intended to provide an exhaustive overview of the entire field of chronobiology or behavioral rhythms. Instead, we invited researchers from a variety of fields to critically review and integrate studies that address the roles of circadian rhythms in behavioral neuroscience. The papers included in this issue range from the molecular biology of clock genes to the behavior of free-living animals, and cover a wide variety of species ranging from insects, to rodents, to humans. As such, the reviews provide an overview of the burgeoning field of circadian rhythms within behavioral neuroscience.