Arbitrators in investor-state disputes plainly owe duties to the parties. They are appointed to do a job and they must do that job and do it well: competently, diligently, ethically, expeditiously, fairly, impartially and independently, and properly. They must act with sound judgment, due care, and an open mind. But do investor-state arbitrators also owe duties to anyone else? If so, what duties do they owe and to whom? From where do such duties originate? Given that party autonomy is a hallmark of arbitration, may duties to non-parties ever prevail over the will of the parties? How are such duties enforced? And, what does the existence of duties to non-parties mean for the system of international investment arbitration? Investment arbitration was born from a party-centric tradition. But it has become clear that tribunal rulings affect non-parties. Scrutiny is needed of the responsibilities the arbitrators owe those outside the room. This article explores this less-trodden terrain. It begins by establishing a beachhead – a clear example of a duty to a non-party, as a proof of concept – before moving into rougher territory. Thus, it opens with an illustration of a duty created by the treaty establishing the International Centre for Settlement of Investment Disputes (“ICSID”): a tribunal must issue a written, reasoned award. After demonstrating that this first duty is owed to ICSID itself as an institution (as well as to the parties), the article adds other duties that investor-state arbitrators owe to arbitral institutions and to non-party participants in investment cases, including other states and non-government organizations. It then introduces the concept of systemic duties, which arbitrators owe not to particular persons, but to the creators of the investment arbitration system (states) and its ultimate beneficiaries (the global public). Finally, the article discusses how recognizing duties to non parties both informs a proper understanding of the investment arbitration system and may help improve that system.