The ‘constitutional failures’ ushering in World Wars I and II and the emergence of post-war ‘multilevel constitutionalism’ in Europe suggest that also UN/WTO law can effectively protect international public goods only if UN/WTO law are interpreted and protected for the benefit of citizens in conformity with the human rights and other ‘principles of justice’ recognized by all UN member states. This paper discusses recent publications by Philip Allott on ‘international constitutionalism’ and argues that the necessary transformation of the prevailing conceptions of ‘international law among sovereign states’ into a ‘multilevel constitutional law of humanity’ requires extending ‘multilevel constitutionalism’ to UN/WTO governance of public goods with due respect for ‘constitutional pluralism’ protecting individual and democratic diversity, subsidiarity and ‘institutional experimentation’.