International and regional governmental organizations are the most durable elements of international governance, both in Europe and beyond; they provide public goods for problems that transcend the national scale in an increasingly institutionalized and authoritative manner. Yet, our knowledge of their design is limited. How do the institutional designs of international and regional governmental organizations vary, both cross-spatially and cross-temporally? Do European governmental organizations with their high degree of authority tend to be rather different from governmental organizations in other parts of the world and globally? How and under what conditions do particular design features emerge? To what extent do European governmental organizations serve as models from which policy-makers draw inspiration (diffusion)? And what are the consequences of particular design choices for their subsequent operation? This panel features five papers that tackle this research agenda in a systematically empirical way, bringing to bear original data on particular features of institutional design of international governmental organizations to test existing theories and develop new ones. Two papers focus on dispute settlement mechanisms and their operation (Bezuijen/Hooghe and Voeten/Grewal); one paper analyzes variation in the access of transnational actors (Tallberg et al.); one paper scrutinizes the determinants of variation in the degree of delegation and pooling in regional organizations (Lenz/Marks); and a final paper considers the relationship between institutional design and politicization of international governance (Rauh/Zürn).