This article examines the role of negative emotions in the process of international mediation. In particular, it investigates how perceptions of disputant negative emotions influence the tactics that mediators employ. Using the classification of mediator tactics into communicator, formulator or manipulator, the article argues that communicator- or formulator-oriented tactics are adopted more frequently when a mediator perceives negative emotions, such as anger or fear. The results of a web survey of North American mediators that classified mediation tactics are presented. The authors also interviewed international mediators and diplomats who have formally or informally, officially or unofficially, mediated intra-state and inter-state conflicts. Mediators are found to be more inclined to assume communicator- or formulator-oriented tactics when confronted with negative emotions. Our empirical analysis of negative emotions sheds light on the choice of mediation tactics in the field of international mediation, and offers valuable insights to scholars and practitioners of negotiation, diplomacy, international relations and political science.