Twenty years of experience have inevitably brought to light challenges and tensions in the enforcement of the European merger control system. Some of these challenges have been faced, some have been solved, and some remain latent. This very valuable study starts from the proposition that the EU has never fully acknowledged those fundamental challenges which relate to the rationale behind merger control in Europe. The author shows how the Commission's focus on adapting the rules of merger control to the economic realities of the future business environment, although designed with a view to facilitating European integration, has compromised attainment of legal certainty, transparency, and welfare enhancement.