The paper delves into the concept of Open Government, analysing and characterising its participatory dimension. It proposes firstly a typology of participatory actions that illustrates the strengthening effect that ICT have on the different participation forms. Secondly, it presents the "Participation Schemas", a conceptual tool that facilitates the analysis and standardized representation of the most important dimensions of participation. Participation Schemas provide both a categorization model that deepens our critical understanding of participation and a powerful and flexible tool for the evaluation, design and communication of diverse kinds of participatory initiatives.