The settlement of international investment disputes between states and investors (ISDS) is currently the subject of reform discussions. Part of the discussion is about the ethics of the arbitrators. On the one hand, the lack of common binding ethical standards that apply to all participants in arbitration regardless of their different legal cultures has been raised in general. Second, among the criticisms related to ISDS are concerns about the lack of separation of roles among actors in arbitrations. Since there is no court with a fixed composition, but arbitral tribunals are appointed on an ad hoc basis, there is the possibility that actors may simultaneously assume different roles in different proceedings (so-called "double hatting"). They may be involved as party representatives in one arbitration and as arbitrators or experts in another dealing with similar or related issues. This could create personal, professional and factual incompatibilities. This is addressed by the system by allowing parties to challenge arbitrators, and a partial tribunal is also a ground for annulment of arbitral awards. Nevertheless, there is public concern that possible incompatibilities are not adequately prevented. Within the framework of UNCITRAL Working Group III, a Code of Conduct for Arbitrators has now been developed in cooperation with ICSID, which regulates these issues. The workshop will discuss this code and compare it with ethical rules for adjudicators at other international dispute resolution institutions.