Law and governance derive their legitimacy and effectiveness from consent and support by citizens and from the transformation of agreed principles of justice into democratic legislation, administration, adjudication and multilevel protection of public goods. The more globalization transforms national into transnational public goods that can be collectively supplied only by means of international law and institutions, the more important have cosmopolitan rights become in empowering and motivating citizens to participate – inside and beyond national democracies – in the collective production of public goods like human rights, rule of law, democratic governance, peace, the global division of labor and sustainable development. Sections I and II discuss moral cosmopolitanism as the foundation of human rights and cosmopolitan principles as integral parts of modern constitutional and international law. Section III describes how economic and political cosmopolitanism can act as drivers for cosmopolitan international law by recognizing and protecting rights and remedies of citizens beyond national frontiers, for instance, in contract, commercial, trade, investment and intellectual property law and arbitration, human rights, labor law and international criminal law. Sections IV to VI explain why democratic and republican constitutionalism must be supplemented by “cosmopolitan constitutionalism” in order to render multilevel governance of transnational public goods more effective. By promoting mutually beneficial cooperation among citizens across frontiers, constituting, limiting, regulating and justifying multilevel governance powers, and empowering citizens to hold multilevel governance institutions legally, democratically and judicially accountable, cosmopolitan rights have constitutional functions necessary for citizen-driven protection of public goods. In a globally integrating world without global democracy and global justice, democratic and republican constitutionalism must incorporate cosmopolitan constitutionalism in order to remain legitimate and democratically capable of protecting international public goods.