The IAP, or Wada test, was originally designed as a method to allow unilateral electroconvulsive shock therapy for psychosis. The method soon proved valuable as a tool for language lateralization1and was used as a screening tool for temporal lobectomy candidates following Penfield and Milner's study2of patients who became amnesic following a unilateral temporal lobectomy in the 1950s. Because there were no other reliable ways of evaluating the form and function of the contralateral structures prior to surgery, the IAP quickly became established as an essential presurgical investigation to screen for amnesic risk. More recently, data from the IAP has been used for a variety of other purposes within the epilepsy surgery setting. This article examines the role of the IAP in each of these domains, with reference to the historical context of the procedure, advances in neuroimaging, the published literature, and our own clinical experience.