This chapter introduces to ontologies as they are used in digital humanities, with some notes on possible future use. It focuses on the relationship between models and the objects being modeled rather than on technical issues connected to modeling. In a well-designed ontology there will be both an anchoring to human understanding through textual scope notes with examples and connections to other concepts through hierarchical links and other relationships. For many in the humanities, “ontology” first and foremost denotes a philosophical discipline, a part of metaphysics studying the nature of being. In the literature about ontologies, one will frequently meet the terms upper- or top-level ontology, domain ontology and core ontology. Both creating and using ontologies will necessarily involve data modeling. Further, data modeling will always involve ontological considerations. A formal ontology aims at expressing someone’s conceptualization of a part of the world. The future development of ontologies is closely connected to the Semantic Web and linked data.