Since 2015, the European Commission (EC) has been advocating the establishment of an investment court system (ICS). A key aspect of the proposal is the creation of the strictest ethical standards ever seen in the field of investor-state arbitration. The exercise of functions as an arbitrator does not traditionally require exclusivity, and many lawyers offer their services in the market in other capacities. This situation is described as the “double hat” phenomenon and is seen as one of the most frequent moral hazards in investment arbitration. Both the Comprehensive Economic Trade Agreement (CETA) and the Commission’s investment chapter proposal for the Transatlantic Trade and Investment Partnership (TTIP) prohibit adjudicators from acting as legal counsel in other investment dispute cases. This article discusses the potential advantages and drawbacks of the EC’s approach to the “multiple hat” problem and their potential impact on the investment arbitration system as a whole.