"European Union Delegations are an integral part of the EU External Action Service (EEAS) and have constituted the official diplomatic representation of the European Union to countries outside of the EU since the signature of the Lisbon Treaty in 2007. However, despite these steps towards further political integration, the Treaty of Lisbon has been unable to streamline differences across third states and the EEAS hence remains a diplomatic service of different speeds.This study considers why the EU centralizes diplomacy more easily in some third countries rather than in others, and offers a systematic answer to this question by analysing the EU Delegations both across time and space, notably by developing a quantitative tool, the EU Diplomacy Centralization Index. The results show that whilst the EU is adept at centralizing diplomacy in developing countries and - quite surprisingly - in countries of strategic/security importance, it encounters difficulties in doing this with major economic partners. "--