The principal role of EEG in focal epilepsy is to assist in diagnosis and classification of epilepsy subtype and identifying and localising epileptic focus. Interictal and ictal EEG patterns both provide very useful information to localise the epileptogenic zone in patients with drug-resistant focal epilepsy, specially those undergoing presurgical evaluation. Scalp EEG, particularly prolonged inpatient video-EEG monitoring, provides very valuable information in patients with drug resistant epilepsy undergoing presurgical evaluation in most clinical situations, whereas intracranial EEG is often needed in a small proportion of patients with drug resistant focal epilepsy undergoing presurgical evaluation to refine the localisation of epileptogenic zone and its relationship with the surrounding eloquent cortex. Advances in AI-driven EEG interpretation hold promise for providing more objective, sensitive, and efficient clinical and research information in the future.