This book examines the coherence of EU external representation at the UN for the period of 1993-2012. it theorizes EU representation into a principal-agent model and adopts a nested analysis to detect the coherence variation in EU representation over time. at the UNGA, EU representation is quantitatively measured in terms of EU voting cohesion. At the UNSC, descriptive statistics are analyzed to capture the voting patterns of the EUMS sitting on the council. Both horizontal and vertical coherences of EU representation are then investigated in the case studies of the Iraq and Libya crises；It is found that EU representation coherence, in general, has increased with the developments of the CFSP throughout a period of 20 years. There formed delegation structure introduced by the Lisbon Treaty, however, has yet to contribute to a more coherent EU. It largely depends on the genuine willingness of EUMS to overcome divergent preferences and to support common EU positions. Only until their declaratory commitments lead to real cooperation can the Union truly stand united and speak with one voice. Of equal importance is the call for closer policy coordination among different EU institutions. Time is still needed for EU representatives，namely the President of the European Council, the Commission President and the refashioned High Representative, to develop into fully-fledged agents with more autonomy and clearer delimitation of representation competences.