Cartel activity is prohibited under EU law by virtue of Article 101(1) of the Treaty on the Functioning of the European Union. Firms that violate this provision face severe punishment (including stiff fines) from those entities responsible for enforcing EU competition law. Such firm-focused punishment is an established feature of the antitrust enforcement landscape within the EU. It is increasingly recognized that punishment for cartel activity should be individual-focused as well as firm-focused. Accordingly, a growing tendency to criminalize cartel activity can be observed in the EU Member States. The existence of such criminal sanctions within the EU presents a number of crucial challenges that need to be met if the underlying enforcement objectives are to be achieved without violating prevailing legal norms. First, the employment of criminal antitrust punishment must be justifiable. Second, antitrust criminalization should only occur in a manner that respects the mandatory legalities applicable to the European jurisdiction in question. Finally, the correct practical measures need to be in place in order to ensure that the employment of criminal antitrust punishment actually achieves its aims while maintaining its legitimacy. This book analyses these three crucial challenges so that the complexity of the process of European antitrust criminalization can be understood more accurately. The book acknowledges that three challenges should not be considered in isolation. There is a dynamic relationship between the theoretical, legal, and practical challenges of European antitrust criminalization and an effective antitrust criminalization policy recognizes and respects this complex interaction.