Twenty-five years ago in Reykjavik, Iceland, US President Ronald Reagan and Soviet General Secretary Mikhail Gorbachev walked to the threshold of a nuclear-free world—and then turned back. Reykjavik has since become synonymous with the unforeseen and anticlimactic in nuclear diplomacy. Another feature of Reykjavik’s legacy is less well-understood—its constructiveness. The authors contend that nuclear disarmament should serve as the public keystone of US efforts to reduce nuclear threats across the board and compare and contrast the geopolitical and diplomatic contexts of 1986 with today. The authors identify three historical parallels—fiscal pressures, nuclear accidents, and missile defense; and they identify three discontinuities—a transition from global bipolarity to multipolarity, a shift in US priorities from arms cuts to nonproliferation, and weakening support for international law in US domestic politics. From this comparative analysis, the authors deem Reykjavik to have imparted three core lessons: Disarmament agreements are achievable if the right conditions exist. Even if unrealized, good-faith disarmament efforts provide the diplomatic framework and global credibility needed for nuclear diplomacy to succeed. And Reykjavik’s successes and shortfalls testify to the crucial importance of leadership in making progress on the entangled matters of nuclear nonproliferation, arms control, and disarmament.