Book excerpt: Competition authorities are increasingly interested in understanding the impact of their activities on markets and consumers. The goal is to improve competition policy rules and decision-making practices and to get robust evidence on the benefits of competition and competition policy for society as a whole. Discussions with competition authorities, practitioners and academics have shown the need to take stock of the experience gained in this field by the European Commission and to present it in an easily accessible way. The studies collected in this volume – prepared by senior Commission officials and competition policy experts – range from the ex post evaluation of specific policy interventions to the assessment of the broader impact of competition policy. The issues and topics examined include the following: objectives and scope of evaluations by the European Commission; description of counterfactual evaluation techniques used; conditions for a successful ex post evaluation of a competition policy intervention; a wide selection of individual cases covering a variety of economic sectors; applications in merger control, antitrust and State aid; direct benefits of competition policy interventions for consumers; deterrent effects of such interventions on market participants; and macroeconomic outcomes in terms of job creation, productivity and GDP growth. This matchless book assembles within a single volume all that is needed for competition policy analysts and practitioners to undertake ex post economic evaluations. While its collection of state-of-the-art ex post evaluation studies has a clear value for competition authorities, it is sure to be welcomed as well by competition law practitioners in the private sector, who will greatly appreciate the effort made to cast a critical eye on decisions taken in the past. Moreover, it allows for addressing some of the new challenges facing competition policymakers. Fabienne Ilzkovitz is Principal Advisor responsible for the economic evaluation of competition policy within the Directorate-General for Competition of the European Commission, and since 2014, she has coordinated various ex post evaluation projects in the Directorate-General. She is also Associate Professor of Economics in the Solvay Brussels School of Economics and Management at the Université Libre de Bruxelles, Belgium. Adriaan Dierx is Senior Expert on ex post economic evaluation within the Directorate-General for Competition of the European Commission. He has managed a number of studies aimed at assessing the economic impact of the European Commission’s competition policy interventions.