Since its inception, open government data (OGD) as a free re-useable object has attracted the interest of researchers and practitioners, civil servants, citizens and businesses for different reasons in each target group. This study was designed to aggregate the research outcomes and developments through the recent years towards illustrating the evolutionary path of OGD portals, by presenting an analysis of their characteristics in terms of a maturity model. A four-step methodology has been followed in order to analyse the literature and construct the maturity model. The results point out the two greater dimensions of OGD portals, naming traditional and advanced evolving within three generations. The developed maturity model will guide policy makers by firstly identify the current level of their organisation and secondly design an efficient implementation to the required state.