One of the central difficulties in managing global commons problems is that the relevant actors often do not know which actions to take nor the cost and impact of changing behavior. This problem of uncertainty can often impede cooperation, especially when actors are risk averse and when incumbents are well-organized to block policies that could undermine their market position. Drawing from the literature on experimentalist governance (XG), Victor will explain why some areas of coordination on climate policy—for example, on forests and on expansion of renewable energy—are moving quickly even as most others remain entrenched. This talk will present the opening chapter from a book Victor is finishing with Charles Sabel, and will focus on the implications of XG thinking for international cooperation theory as well as the fate of the Paris Agreement and other climate institutions. It will also suggest, by reexamining history, that many of the iconic examples of successful international governance—such as in trade and in protecting the ozone layer—owe their success to XG-like institutions.