The OECD Competition Committee held a roundtable on Impact Evaluation of Merger Decisions in June 2011. This document includes: an executive summary and an aide memoire of that discussion; written submissions by Belgium, Brazil, Canada, Chile, Estonia, Greece, Hungary, Indonesia, Japan, Korea, the Netherlands, Norway, Poland, Romania, South Africa, Switzerland, the United Kingdom, the United States, the European Union and BIAC; as well as additional contributions.