The dynamic state of sleep offers unique diagnostic and therapeutic opportunities for diseases of the central nervous system, such as epilepsy. Sleep encompasses neurophysiological states that may reveal aspects of epilepsy that are not readily apparent in wakefulness. Sleep deprivation is accepted as a provocative agent for seizures and epileptiform activity. In addition, the treatment of sleep disorders may provide beneficial effects to the brain to improve the control of seizures and quality of life. Beyond sleep, the circadian rhythm may influence the timing of seizures and medication pharmacokinetics and effect. Epilepsy and its treatment may also influence sleep. Epileptic discharges can change the brain’s sleep regulatory mechanisms, increasing shifts in sleep stages and arousals. Moreover, the treatment of epilepsy may alter the brain’s sleep regulation.