Everyone is talking about international constitutional law: but several different conversations seem to be going on. A first conversation concerns how international law is developing its own constitution, and a second how domestic constitutional law is internationalising under supranational and transnational pressures. This article adds a third conversation concerning how international law regulates the framing of new or revised polities and their constitutional orders, which has largely been an outlier due to its lack of clear disciplinary frame as either international law or constitutional law. The article explores whether these different conversations, often assumed to be part of a common field of study, in fact talk to each other. Are they one or many? In conclusion it is suggested that the ‘lonely third’ conversation makes explicit a converging consensus across all three conversations, revolving around the idea that constitutional orders in either the domestic or international domain are shaped and made normative by the dialectical interaction between them. This converging consensus not only links all three conversations, but stands to re-work our conception of constitutional foundations in more traditional settled domestic contexts.