The epileptic encephalopathies are severe childhood disorders characterized by epilepsy with developmental delay and/or intellectual disability. These disorders were largely unexplained until recently. Improved genomic techniques have now allowed us to identify new genes involved in these disorders. However, the functions of these genes remain unknown. We study the roles of these genes during the development of inhibitory neurons that are essential to prevent excessive brain excitation and seizures. For this purpose, we use a combination of genetic techniques and imaging in embryonic mice brains and investigate the way inhibitory interneurons migrate and mature. These experiments will help us clarify the mechanisms by which mutations in these new genes cause epilepsy and will help develop better therapies for children with epileptic encephalopathies.