This article examines the relationship between sleep and epilepsy, an association that has been recognized since antiquity. The mechanisms whereby sleep facilitates seizures are under investigation, although the synchronizing role of thalamocortic networks seems contributory. Recognition of the variety of generalized and partial epileptic syndromes associated with sleep, familiarity with the differential diagnosis of nocturnal spells, and awareness of the role that antiepileptic drugs and sleep disorders may play in epilepsy are helpful in evaluating patients presenting with behavioral and motor disturbances of sleep.