The efforts to harmonize the practice of international tax policy have, unfortunately, received scant attention from students of international relations. The debates among scholars of international tax law range from disputes over the conditions that will foster an acceptable and effective international tax regime to the very existence of such a regime. This debate finds its analogue in the split between the pluralists and solidarists within the English School. The debate over tax harmonization provides an opportunity to empirically evaluate these two diverging points of view within the English School. Conversely, the application of the English School framework to tax harmonization contributes a theoretical element heretofore absent from the international tax literature. Drawing upon an examination of published and archival material from the negotiations over the United Nations Model Double Taxation Convention and the OECD Model Tax Convention on Income and Capital, this paper finds that the twin institutions of nationalism and sovereignty are central to understanding the successes and failures of international tax harmonization efforts.