This paper develops the concept of the monopoly of jurisdiction of the Court of Justice of the European Union (CJEU) through the analysis of the case-study of the recently challenged Investment Court System. By providing a general framework over the criteria which have been developed by the Court, the work intends to be both pragmatic and theoretical. One the one hand, the criteria are developed as operative tools extracted from the jurisprudence of the CJEU, which are then applied to answer the specific question of the validity of the Investment Court System under the light of such monopoly. On the other hand, the paper questions the reasoning behind such idea of monopoly and discusses the concept of autonomy of the European Union as a claim for power of the CJEU, criticizing the legitimacy of its foundations. Both dimensions will hopefully help to provide some clarity over the meaning of the monopoly of jurisdiction, while at the same time promoting a larger discussion on its impact on the external action of the European Union.