Genetic and molecular biological methodologies are being applied to the study of patients with epilepsy at an ever-increasing pace. Accurate classification of epilepsy within large families has allowed identification of genes through linkage analysis and then isolation of gene products. Mutations causing ion channel abnormalities coupled with clinical patterns of focal epilepsy syndromes are beginning to change our thinking about the etiology of recurrent seizures in all patients. Molecular methodology is beginning to have impact on understanding of the mechanisms of actions of drugs used to treat epilepsy and will have an impact on how future treatments are designed.