This paper argues that domestic arrangements are not only changed by formal international norms. They are also transformed by State narratives as to why these norms should have authority within their territories. This is particularly so with regional trade agreements. Authority for their wide-ranging claims to obedience cannot provided by the meagre gains supplied by regional trade liberalisation. Significant regional trade arrangements seek authority, instead, by setting out models of Statehood for the region. Two ideal types have emerged, that of a civil order and that of the investee State. Through comparing Mercosur and ASEAN, this paper shows how these narratives lead not merely to different types of market, but different conceptions of the separation of powers, executive formation, regulatory styles, public discourse, and relations to foreigners. It concludes that the rise of the investee State narratives poses one of the most significant constitutional challenges of our time.