ICSID prescribes that the ICSID arbitrator must ‘be relied upon to exercise independent judgment’. This chapter begins by comparing this requirement with the formulation found in other arbitral rules and various national laws. It then considers the decisions in both ICSID and other arbitrations concerning challenges, based on (i) the relationship between an arbitrator and a party; (ii) the relationship between an arbitrator and a counsel; and (iii) issue and subject matter conflict. The chapter concludes by recommending that the legal test and procedure for determining arbitrator challenges in ICSID proceedings should be changed.