Immediately after the terrorist attacks on the Pentagon and World Trade Center, NATO members unanimously voted their support for the United States under Article V of the Washington Treaty. This unprecedented action, the first time such a vote has occurred in NATO's history, underscores the vitality of the Atlantic Alliance and its tremendous strategic value for its members. This vote conferred great legitimacy upon any response that the United States will make to those attacks and reminded us that the solidity of NATO allows the United States to defend its interests on the world stage with great confidence about European security. Nevertheless, the Alliance is not a wholly untroubled or static relationship. In the first half of 2001, there were numerous public signs of stress among the allies as they faced new challenges. Many of the issues involved in these tensions are particularly important to the future of European security and must be resolved for NATO to move forward and continue playing the role outlined above. In order for members of the Alliance states and other interested parties to explore the issues at stake earlier in 2001, the Strategic Studies Institute, together with Harvard University's Belfer Center for the Study of Science and International Affairs, cosponsored a conference to discuss cardinal issues of the transatlantic security agenda. This report presents a summary and analysis of the conference, which took place at the Belfer Center, on March 26-27, 2001. Although the world and the context within which these issues must be faced have changed greatly since then, the issues have not gone away nor will they do so anytime soon.