The period between the military intervention against Serbia by NATO and the one in Iraq by the US has been a particularly turbulent one for transatlantic security relations. Is the malaise currently affecting the Transatlantic Alliance more serious than ever before and if so why? Will differences in the assessment of how to provide order and stability in the international system as well as in the evaluation of threats and how to respond to them mark the end of the Transatlantic Alliance? Or will the US, NATO, the EU, and EU member states work together, using different instruments and accepting a degree of division of labour, to pacify, stabilise and rebuild troublesome areas as they have done in South-Eastern Europe? This book, with contributions from leading American, Canadian and European scholars, analyses the reasons behind the latest crisis of the Transatlantic Alliance and dissects its manifestations.