Abstract: Questions about the future of US supremacy, the global spread of liberal democracy, and liberal international economic institutions create what we call ‘international regime uncertainty’: doubts about the fundamental principles, rules, norms, and decision-making procedures that govern areas of international affairs. This includes both probabilistic assessments of the risk that prevailing principles and institutions cease to function but also fundamental uncertainty over what alternative institutional arrangements and governing principles may emerge. Irrespective of actual systemic change, international regime uncertainty can affect transnational economic and political activities by increasing structural policy uncertainty and the probability of bargaining failures. The political uproar over energy transition policies that seemingly violate core principles of the international trade regime illustrates these points.