For more than a century, the concept of the epileptic focus, and of the seizures that arise from such brain regions, consisted of a vague notion of one area of the brain that was “injured,” or at least abnormally excitable, that was relatively discrete, and that, if removed, would render the patient seizure free. In addition, it was thought that the seizure was an abrupt and sudden event, either confined to the abnormal region or spreading throughout the brain. It is becoming more apparent from research in several laboratories, partly based on new technologies, that an epileptic region of the brain more likely consists of multiple small distributed hyperexcitable networks. More interesting, perhaps, is that a variety of electrophysiologic changes may be occurring frequently in these regions that move the brain into different seizure probability states that may wax and wane before clinical seizures develop. These abnormal electrical events may include microseizures, or seizurelike electrophysiologic events, which occur frequently in these small regions; clinical seizures may result when these microseizures slowly enlarge, begin to coalesce, and engage more and more of the normal brain in surrounding regions. The implications of this new hypothesis are enormous and are discussed later in this article.