During the last two decades, extraordinary legal developments have taken place at the regional and global level, as the world of international law has become inhabited by a growing number of organizations designed to govern phenomena cutting across state borders and affecting the life and wealth of individuals world-wide. This evolving reality has challenged traditional understandings of international law and increasingly scholars have resorted to the language of constitutionalism to describe the variety of regimes that by now exist beyond the states. The purpose of this essay is to discuss how comparative law can inform the discussion about the alleged constitutionalization of international law and provide insights to understand several features of the structure, functioning and finality of global governance institutions. In particular, the essay argues that a comparative analysis, grounded on historical studies, of experiences of federal governance offers a valuable perspective to analyse the phenomena of transnational governance and suggests that steps should be made to re-evaluate a long thread of legal practice and political thought that, from Althusius to the Federalist Papers, has offered original models and ideas to conceptualize constitutional regimes which were neither national nor international, but rather a mixture of both. Comparative federalism can today supply a rewarding framework to explain the developments occurring on a global scale. Indicating the path for future scholarly research in the field, the essay begins exploring the mysteries of global governance through the prism of federalism, identifies three recurrent features of transnational constitutional regimes -- pluralism, subsidiarity and liberty -- and underlines how these find correspondence in the experiments of federal governance of the past.