Original scientific paper Open Government Ontology proposed in this paper is an extensive ontology aimed at modelling a wide range of Open Government services. Semantic model of the Open Government opens possibilities for the integration with other semantic and information models, and enables semantic reasoning and resource discovery. Characteristics of the Open Government are transparency, participation and collaboration. Main components of the Open Government are Open Architecture, Open Data and Open Standards. Organizational structure of the Open Government consists of the internal government organizations, associated domains and Open (e)Government services. Open Government Ontology can be used as a semantic meta-data repository for the (e)Government and Open (e)Government services. Using formal methods of reasoning with the proposed ontology we can search for information about Open (e)Government services and infer on gathered knowledge. Also Open Architecture Ontology can be used as Information Architecture framework for the creation of these services as was the case regarding Montenegrin Semantic Science Network.