Socio-economic impact assessment of Research Infrastructures is a fast-growing field. It generates a lot of interest. But it also poses many questions, thus making it a complex topic. This Guidebook is developed for Research Infrastructure managers and staff, policy makers and funders, as well as other professionals who want to develop knowledge on this topic. The Guidebook introduces the language of impact assessment, gives a glimpse into pathways how Research Infrastructures’ activities lead to broader effects on society and the economy, provides useful examples and helps making important strategic choices.