The inheritance of epilepsy has been known since antiquity. Twin studies have shown that genes are important, particularly in primary generalised epilepsies, although the overall risk of epilepsy in offspring of parent with epilepsy is only approximately 6%. Many different protein structures control the normal activation of a brain neurone, and genes are responsible for the structure of these proteins. Mutations can lead to the characteristic pathological activation of epileptic neurones. Monogenic epilepsies may be related to changes in structures of importance for neuronal activation, e.g. the Na channel, the K channel, the GABA-A receptor, and in an acetylcholine receptor. A mutation has been demonstrated in a gene possibly related to brain development. Most likely, many primary epilepsies are polygenic. Epilepsy is also a part of many other genetic diseases. Susceptibility genes may be of importance for the development of certain epilepsies. De novo mutations may also occur. Studies in families with epilepsy may lead to the discovery of more monogenic epilepsies. Comparison between large populations of patients and controls is necessary in order to identify susceptibility genes in non-familiar epilepsy. The new knowledge of genetic aspects of epilepsy will bring improvements in diagnostics and treatment.