Invited Talk by Ian Horrocks Ontologies and ontology based systems are rapidly becoming mainstream technologies, with RDF and OWL now being deployed in diverse application domains, and with major technology vendors starting to augment their existing systems with ontological reasoning. For example, Oracle Inc. recently enhanced its well-known database management system with modules that use RDF/OWL ontologies to support "semantic data management," and their product brochure lists numerous application areas that can benefit from this technology, including enterprise information integration, knowledge mining, finance, compliance management and life science research. While gratifying to the KR research community, this success also brings with it many challenges. In particular, ontology reasoning systems will need to exhibit robust scalability if deployments in large scale applications are to be successful.