A diagnostic scheme for people with epileptic seizures and with epilepsy proposed by ILAE Commission (2001) (Engel, Jr. et al, 2001) newly adopted the concept of “epileptic encephalopathy” as one of new key terms. It is defined as a condition in which epileptiform abnormalities are believed to contribute to the progressive disturbance in cerebral function, but this definition may be ambiguous. The proposal include 8 syndromes; early myoclonic encephalopathy, Ohtahara syndrome, West syndrome, Dravet syndrome, myoclonic status in non-progressive encephalopathies, Lennox-Gastaut syndrome, Landau-Kleffner syndrome, epilepsy with continuous spikewaves during slow-wave sleep. To these syndromes, the migrating partial seizures in infancy and severe epilepsy with multiple independent spike foci (Yamatogi et al, 2006) may be reasonably added. In this chapter, we will concentrate on the epileptic encephalopathies that occur only in infancy. Earlier-onset epilepsy may potentially have a greater impact on a child's development than later-onset epilepsy. Age of epilepsy onset also varies and depends upon the underlying etiology. Seizures and cognitive function may vary over time, depending on the developmental stage of the child. Seizures may eventually remit in many children over time, but behavioral and cognitive problems may persist into adulthood. “Catastrophic epilepsy” is also a collective term for types of childhood epilepsy that take a highly unfavorable course despite intensive treatment, often with polypharmacy (Kramer, 2005). This is understood almost synonymous with epileptic encephalopathy. A common feature is that these disorders are usually refractory to standard antiepileptic drugs (AEDs). As a result, more aggressive use of AEDs considered effective in suppressing interictal epileptiform discharges (eg benzodiazepines, valproic acid, lamotrigine), immunomodulatory therapies (eg, corticosteroids, intravenous immunoglobulin [IVIG], plasmapheresis), ketogenic diet, and surgical options are often considered In this review, epileptic encephalopathies will be dealt in the following concept: a particular group of usually age-related and extremely intractable epilepsies with characteristic generalized minor seizures and massive epileptic EEG abnormalities, both of which cause stagnation/deterioration in mental and cognitive functions in addition to the pre-existing developmental deficit due to organic brain damage.