The neurophysiology of the brain is complicated and nuanced. It is responsible for the normal sleep/wake states that every person experiences, and for the changes in brain neurophysiology that result in epileptic seizures and in disorders of sleep. It is therefore not surprising that sleep, sleep disorders, and epilepsy interact on many levels. The sleep state influences the detection of interictal epileptiform discharges, important for diagnosis of epilepsy. The state of sleep also influences whether a seizure will occur at a given time, and this differs considerably for various epilepsy syndromes. Sleep disruption of any kind, including from sleep disorders, can worsen epileptic seizures and contribute to intractability. Finally, anticonvulsant medications can influence sleep and sleep disorders in both positive and negative ways. Understanding this interplay between epilepsy and sleep is helpful in the optimal treatment of all patients with epileptic seizures.