The present contribution reacts to concerns about the legitimacy of supra- and international public authority by introducing the idea of relative authority. It argues that public authority is relative, first, in the sense that the exercise of authority by one actor always stands in relation to others and, second, that the allocation of authority should be informed by the legitimacy assets that different actors can bring into the governance process. It develops an argument in favor of a specific, articulated allocation of public authority. Like other legal approaches to global governance it is inspired by domestic legal theory and thinking. It distinguishes itself through its focus on questions of institutional choice: Who should do what in European and international law? While ideas of the separation of power face an uphill battle in the variegated institutional settings on the European and even more so international level, the core normative program embedded in this idea provides traction. The contribution offers the idea of relative authority as a core part of an argumentative framework to critique and help justify the exercise of supra- and international public authority.