Constitutionalism was traditionally a domestic law doctrine contending the institutionalization of power, the protection of fundamental (human) rights of individuals as citizens, and the rule of law. Given its value in promoting good governance in democratic societies, constitutionalism has been broadly discussed by international law scholars as a means to promote good global governance. Originally this was limited to human rights, but later extended to other shared values like the fight against nationalism and protectionism. This chapter focuses on the impact of constitutionalism on international economic law (IEL). We consider the role constitutionalism played in the development of international economic law, as well as current criticisms concerning its application in this area. Scholars have tried to link the legal and philosophical ideas of constitutionalism with economic theories, in particular ordo-liberalism which has led to particularly harsh criticism (as it is common in economic theory when it comes to the role of markets and price mechanisms as well as the role of enforceable individual rights [of capital owners and entrepreneurs]). We argue that despite this highly political controversy, constitutionalism had considerably contributed to the development and judicialization of international economic law and will continue to exert an effect on this matter.