Ontologies are becoming so large in their coverage that no single person or a small group of people can develop them effectively and ontology development becomes a community-based enterprise. We present Collaborative Protégé—an extension of the Protégé ontology editor that we have designed specifically to support the collaboration process for a community of users. During the ontology-development process, Collaborative Protégé allows users to hold discussions about the ontology components and changes using typed annotations; it tracks the change history of the ontology entities; it provides a chat and search functionality. Users edit simultaneously an ontology stored in a common repository. All changes made by a user are seen immediately by other users. Collaborative Protégé is open source and distributed with the full installation of Protégé.