Conceptual modeling is often viewed as an activity of representing a preexisting world that should be faithfully mirrored in an information system. This view is adequate for modeling physical domains but needs to be revised and extended for social and institutional domains, as these are continuously produced and reproduced through communicative processes. Thereby, conceptual modeling moves beyond analysis and representation in order to cater also for design and creation. Following such a view on conceptual modeling, this paper proposes an ontology for modeling institutional domains. The ontology emphasizes the role of institutional entities in regulating and governing these domains through rules and rights that define allowed and required interactions. Furthermore, the ontology shows how these institutional entities are dependent on and grounded in material entities. Conceptual modelers can benefit from the ontology when modeling institutional domains, as it highlights fundamental notions and distinctions in these domains, e.g., the role of rights, the role of processes in creating institutional facts, and the difference between documents and institutional information. The ontology is illustrated using a case on public consultation management.