In 1999 NATO will formally admit three new members and adopt a new strategic concept. In so doing, it will take giant strides towards effecting a revolutionary transformation of European security. On the one hand, it could be said that NATO enlargement closes the immediate post-Cold War period that began with the collapse of the Berlin Wall in 1989. But on the other hand, enlargement raises a host of serious new issues for the Alliance and for U.S. policymakers that they must begin to address now. Bearing this fact in mind, the Strategic Studies Institute (SSI) organized a conference with the Center for Strategic and International Studies in January 1998 to explore the new challenges confronting the NATO Alliance. These essays are the product of that conference.