This article takes what has always been a methodological and ethical question for anthropologists (how should we relate to others?) and turns it into an ethnographic one (how do those we study think ethically across borders?). We show that, paradoxically, anthropologists’ commitment to their own forms of ethics across borders have frequently effaced alternative conceptions among the people we study, whilst the burgeoning field of the anthropology of ethics has reintroduced ideas of cultural boundedness and incommensurability into the anthropological canon. Moreover, within anthropology, a focus on either universal motivation or cultural relativism has obscured ethics across borders, which as a practice is premised on both the existence of ethical difference and the possibility of transcending it. In relation to an example taken from Evans’ work on Ahmadi Muslims in India, we develop the idea that ethics across borders depends as much on the creative production and elaboration of incommensurable differencem - a process we call “incommensuration” - as on the identification of affinities. As suggested by the collection this essay introduces, ethics across borders in this sense must be widespread, and deserves greater ethnographic attention, particularly with regard to the diverse ways in which difference and affinity are imagined.