Recent debates in International Relations seek to decolonise the discipline by focusing on relationality between self and other. This article examines the possibilities for preserving a particular type of otherness: 'radical otherness' or 'alterity'. Such otherness can provide a bulwark against domination and colonialism: there is always something truly other which cannot be assimilated. However, two problems arise. First, if otherness is truly inaccessible, how can self relate to it? Does otherness undermine relationality? Second, can we talk about otherness without making it the same? Is the very naming of otherness a new form of domination? This article draws out and explores the possibilities for radical otherness in Sinophone and Anglophone relational theorising. It addresses the difficulties presented by the need for a sense of radical otherness on the one hand, and the seeming impossibility of either detecting it, or relating to it, on the other. By constructing a typology of four accounts of otherness, it finds that the identification and preservation of radical otherness poses significant problems for relationality. Radical otherness makes relationality between self and other impossible, but without radical otherness there is a danger of domination and assimilation. This is common to both Sinophone and Anglophone endeavours.