Sleep disorders are so common that approximately 38% of the general population complains about a current sleep problem and 52% complains about a current or past sleep problem. Psychiatric factors are prominent in virtually all sleep disorders, either as primary factors (insomnia and adult parasomnias) or as significant secondary consequences (sleep apnea and narcolepsy). The authors describe normal sleep; delineate the prevalence of sleep disorders, both those associated with psychiatric disturbance and those of organic etiology; and outline procedures for evaluation and treatment, which is multidimensional and comprises general measures, psychotherapy, and, when indicated, pharmacotherapy.