The presurgical evaluation of patients with medically refractory epilepsy begins with a thorough noninvasive approach, including ictal monitoring with scalp recording technique. The concept of convergence of evidence is used to determine the adequacy of the noninvasive localization. A variety of intracranial electrophysiologic studies can be employed when the noninvasive evaluation is insufficient. Intracranial studies are used for precise identification of eloquent cortex. The ultimate lines of resection are then designed to include as much of the epileptogenic zone as possible, while excluding areas of eloquent cortical function.