Recent advances in our knowledge of the basic mechanisms of EPILEPSY have derived from increasing ability to carry out detailed investigations on patients surgically treated for refractory EPILEPSY. Clinical as well s experimental perioperative investigations divide into three phases: before the surgical intervention (pre-operative studies), during the surgical intervention (intra-operative studies), and on the period when the brain tissue that has to be removed is available for further studies (post-operative studies). Before surgery, structural and functional neuroimaging methods could be used to study the pathophysiological mechanisms of seizures in patients with intractable EPILEPSY. During EPILEPSY surgery, it is possible to insert electroencephalogram electrodes and microdialysis probes into the brain tissues to evaluate constituents of micromilieu and study brain bioelectrical activities. Surgical resection provides tissue that can be used for electrophysiological, morphological, and molecular biological investigations. To take advantage of these opportunities, carefully designed experimental and clinical protocols are crucial to compare the data from various studies to characterize abnormalities in the epileptic brain in order to improve our understanding of intractable EPILEPSY as well as brain function.