Sleep is one of the cardinal symptoms in psychiatry and indeed in medicine as a whole. A good knowledge about the various aspects of sleep is essential for every student of psychiatry. Normal sleep, NREM sleep, and REM sleep, are types of sleep disorder. Behaviorally, sleep is a reversible state of reduced awareness of and responsiveness to the environment. REM sleep is also called paradoxical sleep because brain metabolism is highest in this stage of sleep. This chapter covers the assessment of sleep problems, general approach to the management of sleep disorders, sleep disorders, insomnia due to general medical conditions, sleep disorders related to psychiatric disorders, and effects of psychiatric medication on sleep.