E-participation projects are complex socio-technical constructs integrating different concepts such as participation techniques, stakeholders, objectives, information artefacts, and technical facilities. To conceptualise comprehensive solutions of e-participation projects in a holistic way – i.e. comprehensively integrating the different concepts forming an e-participation project–, enterprise architecture frameworks are increasingly studied. Effective use of enterprise architecture frameworks demands a comprehensive conceptualisation of e-participation projects, which should embark on a common metamodel. In this paper, we study existing conceptual models structuring the e-participation domain and metamodels of enterprise architecture frameworks. From the insights of the comparative analysis, the e-participation metamodel is developed using design science research. The metamodel provides the conceptualisation and taxonomy for an e-participation reference framework to develop comprehensive architectures in e-participation projects. It is presented in a UML 2.0 diagram and involves six viewpoints: Participation Scope, Participant Viewpoint, Participation Viewpoint, Data & Information Viewpoint, E-participation Viewpoint, and Implementation & Governance Viewpoint.