The thesis analysis the institutional innovations of the external representation after the Treaty of Lisbon, taking into account the often expressed concern of a ?unified voice? for the European Union on the international stage. The High Representative of the Union for Foreign and Security Policy, the new permanent President of the European Council and the European Commission are going to be individualised as the central Organs of external representation. With regard to the question of uniform representation, their duties as well as their cooperation will build the focus of the work. In addition, the work deals with the genesis of the European External Action Service and the institutionalisation of the EU-Delegations. It will be shown, how the decentralised organs of external representation improve the visibility and the influence of the EU in third states and at International Organisations. In the second part of the work, the new system of external representation will be put to the test in the central areas of external action ? the conclusion of international agreements and the cooperation with International Organisations. In relation to the EU?s role while concluding an international agreement, it will be demonstrated, how the treaty provisions divide the task of negotiating between the High Representative and the Commission. Moreover, it is explained, why in practise there exist further constellations of negotiating delegations for mixed agreements. In conclusion, the Union?s relations with international Organisations are pictured. It is illustrated, why the EU possesses no single status in international Organisations and how it is possible, despite the lack of participation, to gain influence, particularly in the light of the new external representation system.