Transnational Economic Constitutionalism Since the 1920ies, the concept of the Economic Constitution (»Wirtschaftsverfassung«) has been highly influential in German and European legal thinking. The Economic Constitution refers to the mandatory legal rules which shape the relationship of economy and politics within a democratic society. In Europe, these norms have come to be defined on a supranational level. Here, the Four Freedoms and the competition rules of the EU Treaty are the cornerstones of a European Economic Constitution. On the international level, there is no equivalent to such norms. World trade and investment law enshrine free trade, whereas there is an apparent lack of even basic rules of market regulation. The practice of cross-border economic exchange can be described as »private ordering in the shadow of law«. Rules from different legal sources are recombined – or even replaced – by private mechanisms of dispute-resolution and standard-setting. The article analyzes this development with a view to the rise of international commercial arbitration and the growing importance of international accounting standards. Both examples show the limited reach of domestic and supranational Economic Constitutions, as they can be employed for »opting out« of mandatory regulation in cross-border contexts. At the same time, however, the institutions of private ordering described here increasingly develop their own standards of mandatory law, both by referring to existing national, supranational and international norms and by generating new rules of a genuinely transnational character. The article argues that these rules may form the nucleus of an emerging Transnational Economic Constitution ordering the relationship between economy, politics and law on a global level.