Sleep disorders are conditions that prevent a person from getting a restful sleep and as a result can cause serious physical, mental and emotional problems. Sleep disturbance accompanied most of psychiatric illness. Prevalence of sleep disturbance in psychiatric conditions can reach up to 80% as in major depressive disorders. Sleep disorders have complex relationship with psychiatric condition. It can be a cause or a predictor of medical, neurological or psychiatric illness. The good news is that all sleep disorders are treatable and can improve quality of life and the course of psychiatric illness. The most common sleep disorders are: insomnia, sleep apnea, restless leg syndrome, parasomnias and hypersomnia like narcolepsy. Most of the sleep disorders can be diagnosed by careful history and examination and some patient will need sleep study. The wide need of sleep medicines, severe shortage of centers and technologies impacts the understanding of sleep disorders.