This study examines the effects of ethnic and social identities on negotiation decision making in the context of the Cyprus conflict. I conduct a theory-driven case study of the 1959 Zurich-London agreements on Cyprus, analyzing the positions of Turkey, Greece, Britain, and the Turkish and Greek Cypriot communities during the negotiation process. I find that even in the presence of adversarial ethnic ties, decision makers who have a shared (and salient) social identity are more likely to employ collective-serving decision strategies and seek evenhanded solutions that will not jeopardize their mutual interests. In contrast, decision makers with severe ethnic fragmentation with no shared social identity (as with the Turkish and Greek Cypriot communities) are more prone to employ self-serving decision strategies and seek zero-sum negotiation outcomes that will exclusively benefit them.