Together with the future enlargement of the European Union, the integration of Hungary, Poland, and the Czech Republic into NATO will significantly diminish the prospect that Central Europe will again become a source of international tension and geopolitical rivalry. However, the entry of these three countries into NATO does not end the process of enlargement. At the Madrid Summit, the Alliance agreed to maintain an "open door" to new members. This raises new policy dilemmas for NATO, from who should next be invited to join, when that invitation should be issued, what effect further enlargement will have on NATO cohesion and military effectiveness, and most important, how enlargement contributes to NATO's overall transformation and new missions. Many factors argue for a deliberate, measured approach to further enlargement, one that gives NATO time to sort out its strategic priorities. At the same time, NATO needs to enhance the credibility of the open door by identifying concrete steps that will ensure that the door truly remains open.