Status epilepticus (SE) is a condition wherein epileptic seizure discharges are sufficiently prolonged or repetitive so as to produce persistent alterations in neurologic function and in the underlying physiologic and neurochemical activities of the brain. Thus, the definition of SE now includes any disorder in which there is sustained and prolonged excitation of neurons. Electroencephalographic (EEG) patterns associated with specific types of SE are important components in their classification. Like epileptic seizures, SE can be divided into partial onset SE and primarily generalized SE. Partial onset SE includes secondarily generalized convulsive SE (GCSE), complex partial SE (CPSE), simple partial SE (SPSE), and the syndromes of epilepsia partialis continua (EPC) and rolandic SE (RSE). Primarily generalized SE includes primarily GCSE, absence SE, atypical absence SE, generalized myoclonic SE, generalized clonic SE, generalized tonic SE, atonic SE, and the syndromes of electrical SE of sleep (ESES) and minor epileptic SE of Brett. SE is a dynamic disorder. Behavioral and electrical manifestations change over time if seizure activity is allowed to persist without successful treatment A progression from overt to subtle convulsive activity occurs in secondarily GCSE and there is also a progression of predictable EEG changes in prolonged GCSE. CPSE begins as discrete complex partial seizures but also progresses behaviorally and electrically through a sequence similar to that observed in GCSE. Progressive behavioral and electrical changes have not been reported in primarily generalized forms of SE. EEG is an important tool for verifying successful treatment of SE if the patient does not immediately recover neurologic function. EEG recordings also contribute substantially to understanding the mechanisms of, and development of better treatments for, human SE through their use in the study of experimental SE in the laboratory.