Sleep and epilepsy are interrelated. Understanding the relationship between epilepsy and sleep is important for optimizing management of the epilepsy patient in several ways. First, sleep modulates the expression of epileptic seizures and interictal epileptiform discharges. Second, epilepsy and its treatment influence sleep organization and daytime alertness, and may contribute to, or ameliorate, sleep disorders. Finally, treatment of a coexisting sleep disorder may improve seizure control, daytime alertness, and health-related quality of life. In this article, aspects related to the interrelationship of sleep and epilepsy will be discussed and the model of how sleep can interact with a neurological disorder will be illustrated.