Our knowledge of genetic factors influencing expression of epilepsy has increased enormously in the last 10 years. In this article, we review the advantages and problems of population genetics studies, twin studies, and linkage analysis as applied to the study of epilepsy. Population genetics, twin studies, and linkage analysis have placed the evidence for the genetic basis of the generalized epilepsies on a firm foundation. The identification and confirmation of a gene locus involved in the expression of juvenile myoclonic epilepsy and other forms of generalized epilepsy is proof of at least one genetic influence. We also review the evidence that other, still-undiscovered genetic factors might influence the expression of other forms of generalized epilepsy.