Most scholars are inclined to assume that the diplomatic practices of the European Union's member states remain fundamentally unchanged. The EU's Council of Ministers is accordingly seen as a setting where sovereign states speak with one another. Yet if state interaction in the EU is only viewed from this perspective, a number of important qualitative changes will remain underexposed. This article argues that leading political forces in the European states have come to view their nations as anchored so deeply within the supranational institutions of the EU that their diplomats merge the promotion of national interests with those of the Union. In this late sovereign phase of diplomacy, political and legal authorities overlap, territorial exclusivity is replaced with functional boundaries, and states begin to speak with one voice. The article explores three interlinked aspects of late sovereign diplomacy: the teleological interpretation of the EC and EU treaties; the intense socialization of state representatives; and the negotiation process, which promotes national positions as part of a European cause, thereby delocalizing the national interest. While the EU has not rendered national diplomacy obsolete, it has profoundly changed its meaning and consequences.