This paper presents a conceptual querying approach with reference to a document collection where the target is the concepts appearing in documents, rather than the documents in the collection. An ontology formalism and a special notion of ”instantiated ontology” are introduced. The latter is a structure reflecting the content in the document collection in that; it is a restriction of a general world knowledge ontology to the concepts instantiated in the collection. The notion of ontology-based similarity is briefly described and a language for navigation and retrieval of concepts in the ontology is presented.