Alliances have played a central role in the pursuit of inter-communal security throughout history and have been a salient feature of contemporary international relations. The growing complexity of a dynamic strategic environment contests the utility of traditional military alliances. Such alliances, argue some, have proven to be of limited value in an era of complex challenges stemming from the proliferation of WMD, transnational terrorism, failed states, counter insurgencies, environmental degradation and other asymmetrical threats. Nevertheless, interest in alliance-based security arrangements is not waning.While it is unlikely they will simply go away, alliances will undoubtedly need to adapt to the changing security environment and growing diversity of security cooperation. NATO, perhaps the most successful modern-day political-military alliance, has gone through a fundamental post-Cold War transformation and is about to implement a new strategic concept that could well entrench a new standard for future alliances.These onerous changes are shaped by factors within and outside NATO.