Debates about post-Westphalian forms of citizenship play an important role in contemporary political thought. I analyse a significant precursor to these debates, exploring fin de siècle conceptions of racial and imperial political membership. My argument has two main parts. First, I delineate four rival models of imperial citizenship: imperial-statist, institutional-imperial, racial-imperial and racial-isopolitan. Second, I dissect the notion of ‘isopolitan’ (or common) citizenship. Isopolity is a practice, derived from the ancient Greeks, in which independent states reciprocally grant citizenship rights to the members of other independent states, thus creating a loose form of political union. It was adapted at the turn of the twentieth century to theorise future Anglo-American relations. I examine the arguments of some prominent isopolitans, focusing on the constitutional theorist A. V. Dicey. ‘Anglo’ isopolitans challenged the isomorphic relationship between the territorial state, sovereignty and political membership. They did so through constructing a global white supremacist vision.