Epilepsy is a common neurological disorder affecting 0.5-1% of the population. Idiopathic generalized epilepsy (IGE) and Rolandic epilepsy (RE), the most common idiopathic syndromes, are largely genetic and represent prototypes for common diseases with complex inheritance. Rare mutations (mainly in ion channels) have been identified in monogenic IGE or as risk factors in IGE and RE. In approximately 3% of IGE patients, microdeletions have been identified but the vast majority of genetic risk factors predisposing to both diseases remains to be identified.The objective of the ‘Complex Genetics of Idiopathic Epilepsies’ consortium (CoGIE) is to unravel the genetic basis and pathophysiology of IGE and RE. The consortium aims to identify both common and rare disease-relevant genetic variations on a genome-wide basis and to determine the functional role of identified variants. CoGIE exploits anestablished and unique interdisciplinary research network of clinicians, geneticists, biostatisticians, physiologists and neuroanatomists.CoGIE will expand the largest cohorts of well-characterized IGE and RE patients already collected by CoGIE partners and other collaborators within the European EPICURE project. By using a combination of modern genetic techniques, including next generation sequencing, genome-wide association studies, copy number variation analysis, andhigh-throughput SNP genotyping, we will identify and validate the genetic risk factors for IGE and RE. Subsequently, comprehensive biostatistical analysis of the genetic data generated will be applied to explore the common etiological factors underlying IGE and RE. Selected genetic variants will be characterized functionally using automated andconventional electrophysiological tech-niques and expression in neurons, and neuroanatomical studies will determine the neuronal expression patterns of affected genes. We anticipate that our studies will have the power and novelty to reveal new pathophysiological pathways of common idiopathic epilepsy syndromes.