The appropriate role of the courts in controlling the discretion of merger authorities has become one of the key issues in European merger law and policy in recent years. This article investigates judicial review of merger decisions, taking a comparative approach by examining cases from the EU, UK and Germany. We observe an apparent increase in the willingness of the EU and UK courts to scrutinize merger decisions, and a long-standing tradition of close scrutiny in Germany. In respect of the EU and UK, we consider agency theory offers a convincing explanation—that increased scrutiny is explained by the need to enhance the credibility of merger policy. In Germany, the constitutional basis of judicial review differs significantly, and the relatively close scrutiny exercised by the court is better explained by the very different constitutional context.