Nevertheless, few research address the critical evaluation of those processes and official statistics fail to understand the deeper dynamics below the mere adoption of European laws in member States. Our study is based upon mixed methods, combining quantitative data and in-depth analysis, and focusing on a combination of variables rooted in literature: (1) accessibility, re-usability and accuracy of datasets covering a minimum set of relevant issues; (2) systemic transparency, as a complex assessment of data transparency and government transparency; (3) e-government maturity, recalling the historical development of the open data policy and the broader political and cultural contexts; (4) public participation and collaboration in re-using data, explaining the role of citizens, journalists, non-governmental organization and companies. We aim at identifying different models of open data implementation according to specific barriers (technical and/or cultural) and drivers (bottom-up and/or top-down).