During its first fifteen years, the EU's merger control system, unlike most others in the world, offered only minimal possibilities for taking efficiency gains into account as a mitigating factor that might offset the anti-competitive effects of a merger. This book examines the background to a change in the legal framework which occurred in May 2004 with the entry into force of a new Merger Regulation that for the first time explicitly recognises the possibility of an efficiency defence. European Merger Control assesses the likely impact of this new regulation, and discusses the pros and cons of the efficiency defence, how other merger control systems deal with efficiencies, how the investigation process can be organised to accommodate the analysis of efficiency gains and the main theoretical and practical problems which arise when anti-competitive effects have to be weighed against efficiency gains. With contributions from distinguished academics in the field of industrial economics and officials with practical experience of merger control, this book will be of interest to consulting economists practising in the field of competition policy, competition lawyers, micro-economists and officials of competition authorities.