Western military co-operation does not conform to the patterns of multilateral international co-operation characterised European economic integration. As this chapter argues, the process has been marked by an Atlantic paradox: while economic cooperation occurred primarily in European multilateral organisations, effective military cooperation emerged in the framework of an Atlantic partnership characterised by American primacy. Arguing that economic and military security were indivisible for Western policy-makers, this chapter challenges the conventional positions in the international relations literature about the failure of military co-operation to achieve a real measure of integration of national defence efforts in the cold war. The analysis explores the Atlantic paradox resulting in the crucial difference between attempts of western economic integration and military co-operation showing that nevertheless that both developments were intrinsically linked. As this re-examination of these developments shows, the different organisational forms of western co-operation formed part of the same open system of transatlantic governmentality in which western countries bargained across institutional settings and policy contexts achieving a remarkable degree of co-operation both in terms of (European) economic integration and (transatlantic) military co-operation.