The ongoing debate within Working Group III of the United Nations Commission on International Trade Law (UNCITRAL) centers on the issues of arbitrator’s independence and impartiality, which could raise a doubts about the legitimacy of International Investment Arbitration as a system. One of the phenomena currently raising doubts about the independence and impartiality of arbitrators is the practice of “double hatting”. The practice of “double hatting” involves the same person simultaneously serving as arbitrator and party representative in various investment disputes, is one of the most controversial issues in the modern investment dispute resolution system in the context of analyzing the prospects for ensuring the independence and impartiality of arbitrators. The regulation of the practice of “double hatting” is complicated by the lack of a unified and agreed-upon definition of this term and its boundaries. Through an empirical analysis of the practice of dispute resolution mechanisms between states and investors, using traditional methods of deduction and induction, the author delves into the nature and scope of the practice of “double hatting”, examines criticism of current mechanisms for regulating this phenomenon, and evaluates the effectiveness of proposed solutions for reforming the Investor-States Dispute Settlement System from the perspective of this phenomenon, primarily the effectiveness of the draft Code of Conduct for Arbitrators in the Settlement of International Investment Disputes, developed by Working Group III. Clearly, to systematically address this problem and determine the vectors of legal regulation, it is necessary to consider best practices in attempts to regulate this phenomenon, both within the framework of new investment agreements and within institutional, permanent bodies of international justice. The conclusion is that a prohibitive approach fails to address key systemic risks. The problem of “double hatting” has already become systemic. Therefore, a comprehensive and multi-layered approach to regulating this problem is more promising.