in Legitimacy: The State and Beyond, ed. W. Sadurski, M. Sevel & K. Walton. Oxford, Oxford University Press 2019: 223-237. Many claims that international courts (ICs) are illegitimate are related in complex ways – differently in fields ranging from human rights to trade. This is not to deny that some talk of the illegitimacy of ICs is inaccurate or wrong. But it is possible and indeed valuable to develop a coherent account that connects several various usages, so as to specify better, worse and downright mistaken claims concerning the legitimacy of ICs. normative legitimacy provides helpful unity to many of the canvassed forms of legitimacy. The particular substantive normative conception of global justice to be respected and promoted by these institutions is not central to this task. I develop the outline of a theory by drawing on Joseph Raz’ ‘service conception’ of normatively legitimate authority, David Easton’s ‘systems analysis,’ and a cosmopolitan normative theory. Section 1 sketches relevant aspects of Raz’ account of legitimate authority: the service conception. Section 2 lays out some normative standards relevant for the ICs. The next sections then elaborate why, on the service conception, various legitimacy conceptions matter for normative legitimacy: why legality matters (section 3) including some reasons for the (limited) significance of state consent – even by rogue states. Section 4 starts to explore why and when actual compliance is important but not always decisive. Section 5 considers why the performance or effects of an IC matters. [WEB].