Multilateral negotiations frequently bring together over 150 governments to take decisions on global policy for a wide range of transnational challenges – from climate change, to international trade and arms control. Those elected to chair (and sometimes host) these negotiations are an important – but often overlooked – actor. When trusted by delegates, chairs can be a critical factor for the reaching of ambitious agreement. Conversely, when the chair is distrusted, it becomes much more likely that negotiations will end in deadlock or failure. Although frequently cited as important, there is remarkably little understanding on the nature and dynamics of trust in chairs of multilateral negotiations. This dissertation weaves theory from the field of organisational behaviour with case studies and ethnographic research at UN climate change negotiations to elaborate an analytical framework that explains why delegates would (dis)trust a chair, how trust develops over the course of a negotiation process, and the consequences for the process and outcome. It then probes the applicability of this framework to a wide range of multilateral negotiations across a number of policy fields. It concludes that trust is broadly experienced in the same way by diplomats, regardless of whether they are negotiating tons of carbon emanating from their economies or the number of missiles in their stockpiles, but that more work is needed to understand the potential idiosyncrasies that might characterise different negotiation processes as a result of organisational culture and history.