Ontology, in its original philosophical sense, is a fundamental branch of metaphysics focusing on the study of existence; its objective is to determine what entities and types of entities actually exist and thus to study the structure of the world. In contrast, in computer science an ontology is an engineering artifact, usually a "conceptual model" of (some aspect of) the world, typically formalised as a logical theory. Formalising an ontology using a suitable logic opens up the possibility of using automated reasoning to support both ontology design and deployment. The value of such support has already been demonstrated in medical applications, where it has been used to help repair and enrich ontologies that play an important role in patient care.Even with the aid of reasoning enabled tools, developing and maintaining good quality ontologies is a difficult and costly task, and problems related to the availability of good quality ontologies threaten to limit the deployment of ontology-based information systems. This has resulted in ontology engineers increasingly looking to the philosophy community for possible solutions, and in particular as a source of relevant expertise in the organisation and formalisation of knowledge.