Given the current challenges to European unity, in particular Russian aggression in Ukraine and dissent in the European Union over economic policy toward Greece, Europeans should remember that, two hundred years ago, they celebrated together a long-awaited peace, as their statesmen collaborated on a lasting settlement to solve territorial questions and ensure international stability. Revisiting the Congress of Vienna, however, is not an exercise in nostalgia. New works on the Congress underscore the critical international stakes in 1814 and 1815, following two decades of war and revolution, and reveal the complexity of the negotiations, political goals, and the unsettled nature of postwar Europe. The Congress was so successful in solving the existential problems of Europe that Europeans would not fight a comparable war against each other for another century—until the Great War in 1914. The challenges that Europe faced in the twentieth century suggest, in fact, that the type of collaborative diplomacy developed at the Vienna Congress remains essential to limit conflict.