This issue of Medical Clinics of North America is guest edited by Dr. Christian Guilleminault, one of the world's leading experts in the field of sleep medicine. He is attributor of the Christian Guilleminault Award for Research in Sleep Medicine bestowed by the World Association of Sleep Medicine. He has put together an outstanding issue that provides the most essential information for the internist on diagnosis and treatment. Topics such as insomnia, excessive sleepiness, REM behavior disorder, restless legs syndrome, obstructive sleep apnea, narcolepsy, pediatric sleep disorders, cognitive behavior therapy, pharmacologic therapy, sleep as it relates to various major medical disorders, and more.