The European Union’s external action is supposed to be inspired by effective multilateralism, a commitment to cooperate with other multilateral actors and to strengthen them. A study of the eu’s Common Security and Defence Policy’s articulation with those organisations that are identified as its partners for international crisis management shows however the institutional dynamics to be much more ambiguous. This ambiguity appears in both the eu’s strategic culture concerning the use of force in its external action, and the communities of practice formed by personnel from the organisations or their members.