For the past fifty years, international efforts to restrict nuclear weapons have relied on formal treaties, primarily bilateral US-Soviet and US-Russian arms-control and nuclear nonproliferation agreements. These treaties delivered major achievements during the late Cold War and after the collapse of the Soviet Union. In recent years, however, nonproliferation efforts have faced a host of setbacks, including North Korea’s and Iran’s nuclear ambitions. Now, Russia’s invasion of Ukraine threatens to topple the international nuclear order. The Future of the Nuclear Order explores the difficulties facing nuclear nonproliferation and arms-control efforts today, from the immediate consequences of Russia’s actions to deeper tensions that have been growing in significance. Joseph F. Pilat and Nathan E. Busch examine the history of international agreements to prevent the spread of nuclear weapons and to scale back the size of nuclear arsenals, placing old and new challenges in context. They analyze the short- and long-term effects of the Russian invasion on the nuclear order, arguing that although the prospects of formal arms-control and nonproliferation regimes have dimmed, a number of informal and nontraditional approaches remain possible, grounded in mutual interest. Timely and rigorous, this book identifies potential concrete steps that the United States and the international community can take to maintain limited progress on arms control despite significant obstacles.