The alignment of competition rules with Union law as well as the creation of appropriate administrative structures is a particular challenge for the countries of Central and Eastern Europe after long years of planned economies, as they had to develop a competition law regime only in the context of the accession process. This study deals with the approximation of Bulgarian antitrust law to Union law. It comprehensively presents the alignment process, the antitrust law (prohibition of cartels, prohibition of abusive practices and merger control) as well as the application practice and examines their compatibility with the Union rules, the decision-making practice of the European Commission and the case law of the ECJ, respectively. Since there is hardly any relevant literature on Bulgarian antitrust law and its application practice, this academic study on the development of competition law in Bulgaria is also an important source of information for practitioners. This study, relevant for academics and practitioners, comprehensively presents the process of approximation of the Bulgarian competition regime to Union law, the current state of the law and the application practice, and examines their compatibility with Union rules, the decision-making practices of the European Commission and/or the case law of the ECJ.