Wind and solar power are increasingly shaping and transforming power systems in Europe and worldwide. The generation costs of these technologies (as captured e.g. by the LCOE) have experienced a strong decrease over the last few years. Nevertheless, given their unique features (variable and uncertain output, location-specific), wind and solar energy bring specific economic challenges when integrated into power systems. These challenges encompass the so-called “integration costs”, which cover the impact of renewable energies on grids development, balancing and changes in the utilization of the conventional generation fleet. The definition and the range of these impacts are subject to controversy amongst academics and policy advisers. This project aims at better understanding the diverse assessments on this issue amongst experts. Its goal is to initiate a constructive dialogue process, to help developing a common understanding of the different perspectives on integration costs and to discuss the effects of potential political choices. Several analyses have been performed for Germany, France and Japan.