Impact is a central concept in today’s science policy. Researchers and research organisations have to demonstrate impact in their projects and applications, and it has become a central part of all types of evaluations of research. Short “impact case studies” is popular in many countries – but does this really measure impact? What are the experiences with impact case studies? These are central questions at this open seminar organised jointly by the Oslo Institute for Research on the Impact of Science (OSIRIS) and the Centre for Research Quality and Policy Impact Studies (R-Quest).