Journal of International Political Theory, Ahead of Print. Harmony is a generally agreed-upon idea in international and diplomatic discourse. A common theme in multiple traditions of thought, Platonist and Confucian among others, it underlies today’s significant investments in musical activism, cultural diplomacy, conflict resolution and peace building. Yet despite this wide currency and long history, the idea of harmony seldom receives more than liminal attention in political theory. In the context of Western thought, an essay written in the 1830s by (...) the French philosopher Jean Reynaud offers a striking point of departure: Reynaud defines diplomacy as ‘the science of harmony among states’. This article, drawing from Reynaud’s text as well from the wider history of music, art and political thought, maps a series of conceptual fault lines that touch on the concept’s function in international thought; the inscription of difference, dissonance, conflict and even war within the idea of harmony; the hegemonic and imperial temptations harmony encompasses and legitimizes; and the theoretical sources of harmony in nature and artifice. In effect, the concept of harmony offers less a blueprint than a forum for imagining peace. (shrink)