The Conclusion draws together the key themes explored in this book. Highlighting the crux norms of comity, collaboration, and conflict management framed by the conditions of reciprocity, reputation, and repeat play, the Conclusion defends a relational and collaborative conception of the separation of powers. Looking to new horizons, the Conclusion gestures at future lines of research opened up by the collaborative idea, including the possibility of imagining international, supra-national, and transnational law in collaborative terms. It concludes by presenting the fundamental norms of the collaborative constitution as vital in the current moment, but also as a form of ’constitutional capital’. On analogy with the influential idea of ’social capital’, it argues that the unwritten norms of the collaborative constitutional system are a precious constitutional resource we should preserve, protect, and enhance in order to create stable and sustainable constitutionalism for the twenty-first century.