Abstract. The rapid increase in the number and use of biological ontologies necessitates developing systems for their integration. In this paper we present a core ontology for biology, and outline its application for integrating biological domain ontologies. Our ontology rests on a foundational ontology, which offers higher-order categories and a theory of levels of reality. The core ontology is implemented in two separate components, each of which adheres to OWL-DL. These can be used independently with efficient DL reasoners, but they will be most effective when used together, which necessitates working with an OWL-Full ontology. The ontology is freely available from our website at: http://bioonto.de/pmwiki.php/Main/GFO-Bio.