Status epilepticus has been recognized since antiquity. The terms état de mal and “status epilepticus” are derived from the slang used by epilepsy patients housed in Salpêtrière and Bicêtre hospitals in Paris during the 1800s. The definition of status epilepticus has been evolving, and is still not precise. In 1903–04 it was described as a development of epilepsy in which seizures are so frequent that “coma and exhaustion are continuous between seizures.” In 1964 the International League Against Epilepsy adopted the definition “a seizure [that] persists for a sufficient length of time or is repeated frequently enough to produce a fixed and enduring epileptic condition.” 30 min has been the most common specified duration of seizures for the diagnosis of status epilepticus, although a duration of 10 or 20 min has been suggested as well. However, a new set of definitions for generalized, convulsive status epilepticus in adults has been proposed and includes an operational definition (specifying a seizure duration of a least 5 min) and a mechanistic definition. In the future, laboratory tests will provide the means for detecting and defining the critical factors that distinguish a single epileptic seizure from status epilepticus. Recent epidemiological studies suggest status epilepticus occurs in 100,000 to 150,000 people in the US each year, and is associated with substantial morbidity and mortality. Etiology, duration of the seizures, and the patient's age seem to be important determinants of the outcome in status epilepticus.