David Dyzenhaus develops the theoretical basis for a ‘permeable’ conception of the constitution. This conception is developed by way of what Dyzenhaus calls ‘a rather deep dive into an arcane debate between the two great legal positivists of the last century, Hans Kelsen and H. L. A. Hart’. The purpose of that detailed analysis is to contrast the respective ‘functional equivalents they propose to Hobbes’s claim that a social contract explains the unity of political and legal order’. These alternatives are Hart’s rule of recognition and Kelsen’s basic norm. Favouring Kelsen’s dynamic, monist conception of the relation between international and domestic law, and his commitment to the ‘gaplessness’ of legal order, Dyzenhaus ultimately turns to exploring the promise of this conception for an understanding of, both the outward projection of public law norms of a domestic legal order beyond its borders, and the reception, within that order, of norms originating elsewhere.