Evan Fox-Decent defends the basic claim that ‘the state’s public law governing its interactions with non-citizens – the state’s cosmopolitan law – must have a certain outward orientation and representative character if it is to be law, properly so-called’. Drawing on earlier work with his frequent co-author Evan Criddle, Fox-Decent invokes the conceptual vocabulary of the ‘fiduciary criterion of legitimacy’ to denote the stipulation that state action ought always to be intelligible as ‘action made on behalf of or in the name of the individual subject to it’, if it is to be legitimate, regardless of whether this individual is a citizen or an outsider in some sense. He uses a discussion of Joseph Raz’s notion of authority, and of the ‘riveting and intractable’ problem of ‘the non-jurisdictional/jurisdictional distinction to distinguish de facto from legitimate authority’ and on this basis constructs his case for the ‘fiduciary criterion’. When it comes to the outer boundaries of the constitutional order, this criterion functions as a ‘cosmopolitan threshold – not a barrier – that welcomes the entry of peaceful outsiders into sovereign states while empowering states to limit migration when conditions warrant’.