This chapter studies the notion of the rights of defence, providing an overview of those rights and tracing their evolution through the case law of the EU Courts. The rights of defence form part of a category of procedural rights that are of particular importance in EU antitrust proceedings. It is settled case law that the rights of defence in any proceedings in which fines or penalty payments may be imposed, such as those provided for in Regulation 1/2003, are fundamental rights forming an integral part of the general principles of EU law. A violation of a right of defence on behalf of the European Commission can have significant repercussions on Commission decisions finding an infringement of EU antitrust rules, the available remedies varying from a complete annulment of the decision to partial annulments and, exceptionally, fine reductions. It is therefore of no surprise that alleged violations of the rights of defence are systematically invoked as grounds for annulment of Commission decisions before the EU Courts, particularly given that infringements of antitrust rules may lead to the imposition of fines that, due to their severity, are now widely considered to be of criminal nature.