In this article, I argue that because co-nationals have an intrinsically valuable relationship, they have a presumptive claim against interference in their collective affairs. My argument from the claim that co-nationals have an intrinsically valuable relationship to the presumptive claim against interference is threefold, and I set it out in section “From Intrinsic Value to Self-Determination”: firstly, parties to an intrinsically valuable relationship have a respect-based claim to autonomy. Secondly, the relationship between co-nationals realizes some important goods, and collective autonomy (...) is internally related to these. Finally, the fact that co-nationals have an intrinsically valuable relationship, and affective attachments means that they have a strong interest in carrying out certain activities together, without interference from outsiders. In section “Grounding the Presumptive Claim,” I argue that these three grounds cumulatively amount to a presumptive claim to collective autonomy. I outline the implications for the issue of secession. (shrink)