From the end of the Cold War to the terrorist attacks on the United States in September 2001, the NATO Alliance has changed profoundly. This text explores the multifaceted consequences of NATO’s adjustment to new international and domestic political and security realities. Internal Alliance politics and matters of relative power within the membership have strongly influenced contemporary NATO developments. Several major issues challenging the Alliance are examined, including how the impact of efforts to develop an enhanced common European security and defence policy have affected NATO; whether missile defence is driving the US and its European allies closer or further apart; whether the experience of NATO in the Balkans and elsewhere brought alliance members together or made NATO cohesion more difficult to maintain; and in what way the changing role of NATO has influenced American and Canadian participation in the Alliance. An important guidepost to pivotal changes and likely NATO developments, scholars and policymakers of Atlantic and international politics should find this useful.