There is a difference between the normative reasons for endorsing global constitutionalism and the conditions determining its emergence. This article addresses the latter issue. Specifically, the article claims that global constitutionalism rests on an underexplored shift in constitutional imagination. To account for this claim, the article is structured in several parts. It begins by clarifying the meaning of ‘constitutional imagination’. In so doing it builds on Kant’s concept of imagination (‘Einbildungskraft’) and in its reception by Hannah Arendt. The article then illustrates the significance of constitutional imagination by focusing on two major developments in constitutional thinking. The first development involves the shift away from a narrative reconstruction of constitutional authority; the second points to a cosmopolitanisation of constitutional imagination.