The State-centered 'Westphalian model' of international law has failed to effectively protect human rights and other international public goods. Most international trade, financial, and environmental agreements do not even refer to human rights, consumer welfare, democratic citizen participation, and transnational rule of law for the benefit of citizens. This book argues that these 'multilevel governance failures' are largely due to inadequate regulation of the 'collective action problems' in the supply of international public goods, such as inadequate legal, judicial, and democratic accountability of governments vis-a-vis citizens. Rather than treating citizens as mere objects of intergovernmental economic and environmental regulation and leaving multilevel governance of international public goods to discretionary 'foreign policy,' human rights and constitutional democracy call for 'civilizing' and 'constitutionalizing' international economic and environmental cooperation by stronger legal and judicial protection of citizens and their constitutional rights in international economic law. Moreover, intergovernmental regulation of transnational cooperation among citizens must be justified by 'principles of justice' and 'multilevel constitutional restraints' protecting rights of citizens and their 'public reason.' The reality of 'constitutional pluralism' requires respecting legitimately diverse conceptions of human rights and democratic constitutionalism. The obvious failures in the governance of interrelated trading, financial, and environmental systems must be restrained by cosmopolitan, constitutional conceptions of international law, protecting the transnational rule of law and participatory democracy for the benefit of citizens.