Electrical source imaging (ESI) is an advanced EEG analysis technique that can be used in the presurgical evaluation (PSE) of drug-resistant epilepsy to localize the epileptogenic zone. ESI is most commonly performed on interictal EEG and has an accuracy that compares favorably to other investigations in the PSE. Ictal ESI may be more accurate than interictal ESI but is more challenging to perform. ESI is also more accurate when performed on high-density EEG, but there is no consensus on the optimal number of electrodes. Software solutions for automated spike detection and ESI significantly improve the feasibility of ESI in epilepsy surgery programs. ESI has been shown to provide new, nonredundant information and has a significant impact on the clinical management plan, particularly on intracranial EEG implantation strategy. ESI and magnetic source imaging are complementary techniques and should be combined in challenging cases.