This Chapter investigates the systemic role and implications of deference in international adjudication. It argues that existing analyses of international adjudicative deference have been based upon, without explicitly acknowledging, an assumed relationship between the domestic and international legal orders. The Chapter proposes inverting the enquiry. Instead of starting from an assumption as to how deference should be structured, it argues that approaches to deference can instead be analysed and conceptually distinguished by reference to how they structure the relationships between the international and domestic legal orders. The Chapter demonstrates that the three conceptualisations of authority underlying the seven modes of deference introduced intoreflect distinct approaches to structuring the relationship between the international and domestic legal orders. Conclusive approaches disclose a monist view of that relationship, whilst suspensive approaches reflect dualist structures, and concurrent approaches reveal pluralist paradigms. This analysis brings into focus the structural and systemic functions of deference in international adjudication.