Sleep disorders medicine and psychiatry interface in numerous ways. Most psychiatric patients have a complaint about sleep, and regardless of the theoretical orientation of a psychiatrist, understanding of a patient's sleep function is an important part of assessment. The success or failure of treatment will be strongly influenced by the effect of that treatment on the patient's sleep disorder. The psychiatrist can provide expertise in treating patients with primary sleep disorders, offering pharmacologic consultations, and recommending psychotherapy or behavioral management. Conversely, a knowledge of primary sleep disorders should make the psychiatrist a more effective practitioner.