NATO's role in forging European order is undeniable, but the clarity and focus of Alliance purpose has changed considerably since the end of the Cold War. The ramifications of this change are considered via analysis of the trajectory of enlargement and a conceptualisation of the enlarged Alliance based upon English School thinking. Four categories are put forward: these refer to geographic levels of operation, conditionality, legitimacy and great-power management. The argument which emerges from this treatment is that NATO was and remains an essential component of European regional international society but its centrality has been modified both by developments consequent upon the end of the Cold War and the political fall-out of the events of 9/11.