Epileptic disorders are classified as idiopathic when they are genetically transmitted conditions that consist of epilepsy only, with no structural lesions in the brain and no associated neurological deficits, and symptomatic when they result from some other primary brain lesion or insult. Symptomatic temporal lobe epilepsy can be further divided into mesial temporal lobe epilepsy (MTLE), the condition associated with hippocampal sclerosis; lesional temporal lobe epilepsy due to specific identifiable lesions localized to areas that preferentially project to mesial temporal structures; and cryptogenic temporal lobe epilepsy, for which no etiology can be determined. Intensive clinical and basic research on MTLE, perhaps the most common form of human epilepsy, is currently being carried out in epilepsy research centers, and a number of experimental animals models have been developed to help elucidate the pathophysiology of this condition. Animal models are also important for determining how specific lesions induce epileptogenicity, and whether the neuronal mechanisms in mesial temporal lobe limbic structures are the same as those in neocortex. Cryptogenic temporal lobe epilepsy remains a major clinical challenge, and much more information needs to be derived from research on patients before relevant experimental animal models can be created.