This communication addresses the case of the European security and Defence Policy (ESDP) and aims at demonstrating to what extent this policy is an emblematic example of a fundamental question raised by the EU: its legitimization. European defence policy is today torn between the claimed intentions on the European level (reactivity to crisis, coordinated action...) the representations that the member-states develop around this policy. From a comparative perspective between France and Germany, the author analyzes this strain and demonstrates that ESDP fulfils latent functions as a political and symbolic substitute which is at least as significant, if not more, as its manifest functions of managing crisis. First of all, there's a kind of torsion between European discourses around European defence policy and still diverging and nationally anchored representations in France and Germany on ESDP. Then a second level of strain originates between the military capacities proclaimed in the multiple European official documents and those really put at EU's disposal by the member-states. Last but not least, a third level of torsion between European reality and discourses is the crucial issue of the legitimization of this policy before the national parliaments and public opinions. Eventually the legitimizing stakes of European defence policy tend to run up against the lack of a European common identity.