In the last few years, the public enforcement of Articles 81 and 82 EC has been thoroughly transformed: the competition authorities of the EU Member States have become active enforcers within the European Competition Network, the European Commission has imposed more and higher fines than ever before, leniency has become a major instrument of cartel detection, and some Member States have introduced criminal penalties. The overall trend towards more and stronger enforcement of Articles 81 and 82 EC has also rekindled discussion on the old question of how to strike the right balance between efficient enforcement and adequate protection of the rights of the defence. This book brings together six essays which analyse from both a legal and an economic perspective the powers of investigation of the European Commission and the competition authorities of the Member States, and the corresponding procedural rights and guarantees, the use of settlements, the theory and practice of fines and of leniency, and the criminalization of European antitrust enforcement.