Aim. The aim of this article is to review criticaly the Electrical Status Epilepticus in Slow Sleep (ESES) phenomenon from a neurophysiological mechanisms aspect as well as terminological and classification issues.Methods. The review includes all the relevant papers published during the last 43 years on the subject of ESES and Continous Spike – Wave in Sleep (CSWS).These papers were identified in various large databases via the internet.Rewiev and remarks. ESES/CSWS phenomena can be held as a common final pathway originating from different etiologies, including patients with early brain damage (probably involving thalamic structures), but also patients without structural pathology as in atypical evolution of idiopathic regional childhood hyperexcitability syndromes (with Rolandic epilepsy as a prototype). There are hints that genetic predisposition might be an important factor in the development of this process. The two large patient groups (lesional and non-lesional) show the same EEG evolution and encephalopathic cognitive consequences. The sleep EEG activation can be held as a common endophenotype. ESES represents an extreme sleep activation/potentiation of the local/regional interictal discharges, enhancing them in frequency, territorial extension, intra and trans-hemispherial propagation, synchrony and continuity. This process is most probably not identical with the development of bilateral spike-wave pattern in „generalized” epilepsies which involves primarily or secondarily the thalamocortical system as it had been explored by Gloor (1979) for idiopathic generalized rpilepsy and Steriade and Amzica (2003) for different types of generalized spike and wave discharges.Conclusions and syndromological embedding of ESES. In an overwhelming majority of the investigated cases, the maps of the single discharges constituting sleep activation are identical; with focal/regional interictal spikes followed by slow closing wave, as it is seen in childhood regional age dependent hyperexcitability syndromes (prototype of the centro-temporal spikes of Rolandic epilepsy). The main mechanism of the developing cognitive impairment is most probably the consequence of interference with plastic function of slow wave sleep by obliterating synaptic decline during sleep. Presently, the consensus and co-operative research is highly obstacled by the terminological chaos, the controversial definitions and views around this still striking and enigmatic phenomenon.