Introduction. The proliferation of bilateral investment treaties in the late 20th century has led to a proportional increase in the number of disputes between investors and host states.

   Materials and methods. Based on traditional methods of system analysis, deduction and induction, scientific analysis, but also system analysis of various international acts, decisions of investment arbitrations and national courts, the author forms the vectors of research of the complex and sometimes contradictory practice of implementing the procedural principles of independence and impartiality in the field of investment arbitration.

   Discussion. According to the standard provisions of investment treaties, disputes between states and investors arising from them were subject to referral to ad hoc arbitration, created on the model of international commercial arbitration. However, the overwhelming majority of claims filed by investors concerned not violations of investment contracts, but rather challenges to general measures taken by states to regulate their economies. Traditionally, such measures were challenged in national courts, but the practice of considering them in investment arbitrations quickly revealed a number of problems directly related to the specifics of the formation of such arbitration tribunals. As a result of the emerging practice, investment arbitration found itself in a deep crisis of legitimacy for the reasons set out in the study. The ways out of the crisis necessitated identifying its causes and making attempts to resolve them.

   The main results. The issues of independence and impartiality of arbitrators in resolving investment disputes are a legitimate concern for states that have allowed, in their international treaties, disputes between investors and the state to be considered not in national courts but in special ad hoc arbitration. This problem has become particularly acute in light of the obvious tendency of investors to refer disputes related to the adoption by states of general measures taken for public purposes and aimed at regulating the economy to arbitration. States have approached the issue of resolving the problems that have arisen in different ways. The nearest future will show the real impact of the adopted Code of Conduct for Arbitrators in Resolving International Investment Disputes on the perception of the parties to the dispute as to what level of impartiality the arbitrators should have and on the tendency to increase the disqualification of arbitrators on the grounds of their bias.