Interactions between International Investment Law and Constitutional Law: Promoting the Dialogue. A European Perspective on Judicial Cooperation and Deference

There are manifold constellations of potential conflict between international investment law and constitutional law. The ordering paradigm for that interaction is an unresolved and underexplored question, which is currently coming up in a number of proceedings. As prominently evidenced by the recent Achmea judgment, we seem to be steering towards supremacy claims of one system over the other with each adjudicative body claiming the final say in the matter. This approach is in line with the classic ordering paradigm of hierarchy. However, this contribution shall argue that hierarchy is ill-suited to properly conceptualize the relationship between the two systems. Instead, it proposes to embrace the heterarchical reality, along with its call for judicial dialogue, as a normatively desirable paradigm. The relationship between international investment law and constitutional law need not be and should not be perceived as inherently antagonistic because their mutual endeavour is to promote the rule of law. Precisely this realization should guide the relationship between the two systems.