Epileptic encephalopathies are conditions in which neurologic deterioration is attributable entirely or partly to epileptic activity. It can be due to very frequent or severe seizures and/or to subcontinuous paroxysmal interictal activity. The former mainly consists of Dravet syndrome, in which patients have seizures from the middle of the first year of life and repeat episodes of severe febrile status epilepticus and migrating partial epilepsy in infancy, in which from the first trimester of life, partial seizures affect various areas of the cortex randomly and in a subcontinuous fashion. In Rasmussen syndrome, also, epileptic activity contributes at least partly to the neurologic deterioration. Subcontinuous paroxysmal interictal activity affects newborn infants with suppression bursts, thus consisting in either Ohtahara syndrome or neonatal myoclonic encephalopathy. In infants, it is either myoclonic epilepsy of nonprogressive encephalopathy or West syndrome. In school-age children, it consists of various types of generalized seizures combined with slow spike waves of the Lennox-Gastaut syndrome, myoclonic-astatic epilepsy, and continuous spike waves in slow sleep combined with various motor or cognitive deficits including negative myoclonus, orofacial dyspraxia, Landau-Kleffner syndrome, and frontal lobe syndrome. Treatment differs for all of these syndromes. It is important to avoid potential drug-induced worsening, and valproate is preferred when a definitive diagnosis is not reached in children and especially infants.