The objective of surgical treatment of epilepsy is seizure control and improvement of quality-of-life of patients with medically intractable epilepsy. Confirmation of the diagnosis of epilepsy and its medical intractability is the essential prerequisite for epilepsy surgery. After excluding nonepileptic events such as psychogenic pseudoseizures, the clinician must establish that adequate drug trials, including verification of compliance, have been performed. A careful diagnostic evaluation is mandatory to localize the epileptogenic zone. In this review we discuss the role of different diagnostic methods with respect to patient selection and surgical outcome. Furthermore, experimental approaches are mentioned and the reasons for failures of epilepsy surgery are critically discussed.