This essay seeks to provide a counterbalance to the frequent push for greater uniformity in international arbitration law. The New York Convention and the UNCITRAL Model Law both have made international arbitration law more uniform, and that increased uniformity no doubt has benefited parties and the system of international arbitration as a whole. But in deciding whether to make further reforms to international arbitration law, policy makers must do more than simply accept that uniformity has benefits. Rather, they must evaluate whether, given the degree of uniformity already achieved, what the marginal benefits of additional uniformity are. And while uniformity benefits parties by reducing the costs of transacting, it also has costs: the loss of individualized fit of laws and reduced legal innovation. The overall question for policy makers, then, is what is the optimal uniformity (or optimal diversity) of international arbitration law? That is a question this essay cannot even begin to answer.