This paper attempts to make sense of Abbé Sieyès’ classical conception of the nation as the constituent power underlying a constitutional system. It then goes on to explore whether it is possible to conceive of such a power under trans- or post-national conditions. What, if anything, might be the power constituting transnational sites of authority, which are by definition not linked to a particular people? The answer to this question requires a modified understanding of collective self-determination. It will be seen, however, that ‘constituting’ does not amount to the same thing in a national and in a transnational context.