The group of idiopathic epilepsies encompasses numerous syndromes without known organic substrate. Genetic anomalies are thought to be responsible for pathogenesis, with a monogenic or polygenic model of inheritance. Over the last two decades, a number of genetic anomalies and encoded proteins have been related to particular idiopathic epilepsies and epileptic encephalopathies. Most of these mutations involve subunits of neuronal ion channels (e.g. potassium, sodium, and chloride channels), and may result in abnormal neuronal hyperexcitability manifesting with seizures. However non-ion channel proteins may also be affected. Correlations between genotype and phenotype are not easy to establish, since genetic and non-genetic factors are likely to play a role in determining the severity of clinical features. The growing number of discoveries on this topic are improving classification, prognosis and counseling of patients and families with these forms of epilepsy, and may lead to targeted therapeutic approaches in the near future. In this article the authors have reviewed the main genetic discoveries in the field of the monogenic idiopathic epilepsies and epileptic encephalopathies, in order to provide epileptologists with a concise and comprehensive summary of clinical and genetic features of these seizure disorders. (C) 2011 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.