This issue of Neurologic Clinics, guest edited by Dr. Phyllis C. Zee, with consulting editor Randolph W. Evans, will focus on Circadian Rhythm Disorders. Topics include, but are not limited to, Circadian biology, Genetic basis of circadian rhythms, Implication of circadian rhythm misalignment on sleep and health, Assessment of circadian rhythms, Circadian Rhythm sleep-wake phase disorders, Irregular sleep-wake rhythm sleep -wake disorder, Non-24 hour sleep-wake rhythm disorder, Shift Work Sleep Disorder, Challenging cases, and Future of circadian and sleep medicine.