The EU-funded project PROSO (coordinated by DIALOGIK) has published a Support Tool for promoting engagement of citizens and third sector actors in research and in research and innovation policy. Its main target groups are policy makers and governmental agencies, research funding organizations and research councils, research organizations, other engagement performing organizations, and third sector actors (such as civil society organizations) at national and European Union levels. These actors can make valuable contributions to promoting societal engagement in research-related processes. The document identifies important barriers to engagement and offers a range of policy options and inspiring practice examples to lower or overcome these barriers. The Support Tool is the main outcome of the PROSO project.