This study is meant to support the European Commission White Paper on Private Antitrust Damages Actions (April 2008). Coordinated by Andrea Renda, it was completed in collaboration with LUISS Guido Carli University (Roberto Pardolesi, Enrico Leonardo Camilli, Paolo Caprile) and Erasmus University Rotterdam (Roger Van den Bergh, Sonja Keske). The study assesses the potential impact of more effective private antitrust enforcement in Europe, and then performs a cost-benefit analysis of selected options related to multiple damages, fee-shifting, access to evidence, group litigation, limitation periods, the legal treatment of passing-on and the coordination of private antitrust damages actions with leniency programs. The study provided a major contribution to the Commission White Paper, as was judged as one of the most refined and ambitious impact assessments carried out at EU level to date.