Pharmacologic therapy represents the first line of treatment of epilepsy and is effective in most patients. However, about 20% to 30% of cases develop intractable seizures that cannot be controlled by medication alone. In such cases, surgical intervention is considered for therapeutic, often curative purposes. Dynamic spatiotemporal variability in the epileptic focus renders seizure localization a challenge to the clinician. Many diagnostic modalities have been developed to identify different aspects of the epileptic focus. Older techniques are being increasingly supplemented by a variety of anatomic and functional imaging modalities that can help clarify discrepancies. Invasive electroencephalography remains the gold standard for identifying epileptic foci and guiding the surgeon to successful resections.