The Epilepsy Ontology (EPIO) is an assembly of structured knowledge on various aspects of epilepsy, developed according to basic formal ontology (BFO) and Open Biological and Biomedical Ontology (OBO) Foundry principles. Entities and definitions are collected from the latest International League against Epilepsy (ILAE) classification, as well as from domain-specific ontologies such as Epilepsy Ontology (EPILONT), Epilepsy Syndrome Seizure Ontology (ESSO), Epilepsy Semiology(EPISEM) and Epilepsy and Seizure Ontology (EPSO) and scientific literature.This ontology is intended to be used for data management and for text mining purposes. The current release of the ontology is publicly available and is a community based effort to assemble various facets of the complex disease Epilepsy.EPIO by SEM-Group of Fraunhofer SCAI is licensedunder CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).