This article investigates the role that diplomacy—especially at the highest levels—can play in transforming adversarial relationships. Building on Martin Wight's exploration of these issues, in particular the question of how two adversaries can convince each other that they are serious negotiating partners, the article contends that achieving a significant de-escalation of a conflict depends upon the growth of trust. In contrast to Wight's limited conception of what diplomacy could achieve in terms of ending conflicts, the argument made here is that particular types of communicative encounters between diplomats, and especially leaders, can build a level of trust at the interpersonal level which can lead policy-makers to make conciliatory frame-breaking moves. To make good on this claim, the article employs a case-study of the summitry between US President Ronald Reagan and his Soviet counterpart, Mikhail Gorbachev. The key contention here is that the face-to-face encounters between Reagan and Gorbachev promoted a level of trust between them that made possible the fundamental de-escalation of the Cold War that took place in the second half of the 1980s. Rival explanations focusing on nuclear weapons and Soviet economic decline are analysed, but while these were enabling conditions in the transformation of relations, the article argues that it is necessary to recognize the critical role that interpersonal trust between US and Soviet leaders played in achieving this diplomatic transformation.