Abstract From a political viewpoint, the external representation of the European Union is an extremely sensitive topic, affecting the visibility and role of European institutions and Member States on the international scene. From a legal perspective, this topic is particularly challenging, since the EU Treaties, as amended by the Lisbon reform, are not completely straightforward in this regard. Such combination of political sensitivity and legal uncertainty renders the Union's representation very contentious. This area has therefore seen not-so-hidden "turf wars" that damaged the image and effectiveness of the EU's external action. The article analyses the issue of the Union's representation with respect to the conclusion of international instruments and, in particular, international agreements. This topic has been profoundly affected by the Lisbon reform, which explicitly provides that the European Commission and the High Representative shall ensure the Union's external representation, in non-CFSP and CFSP areas, respectively (Arts. 17 and 27 TEU). This reform seems to enhance the consistency and unity of the Union's representation and of the Union's ability to carry out effective negotiations, by fostering the self-representation of the Union, with the exclusion of any role previously held by Member States and the rotating Presidency.. The analysis brings to light the two factors preventing the reform from fully achieving its objectives in practice. First, Member States sometimes favour the mixed form of international agreements, even when it would not appear to be strictly necessary. Secondly, Member States seem not to fully accept the consequences of the Treaties' reform and often rely on pre-Lisbon practices, which no longer have any legal ground.