The notion of supply chains has been current for some time in the literature and in practice. Recently this has been extended to consider so-called extended enterprises. The paper considers extensible ontologies as a principle for integrated information and knowledge management and for knowledge sharing. Providing links between companies for the purpose of supporting extended products requires a degree of information and knowledge sharing that that is not adequately addressed by current ERP systems. This paper will consider some of these issues and indicate an approach being explored within the context of a research project funded by the European Commission.