Now that more than thirty years have passed since the fall of the Berlin Wall, it is clear that, while some borders have disappeared, new fronts have appeared as well. And, rather than a “new world order,” a familiar antagonism between Russia and the West is once again asserting itself. Among the central points of dispute is the question of whether the West offered Moscow assurances in 1989-90 in the form of a NATO non-expansion guarantee. Diverging interpretations of this crucial development continue to hinder international understanding and dialogue. In this chapter, Sarotte draws on elements of her historical research into archives in six countries to present evidence on what actually transpired, and to discuss the following questions: To what extent do current challenges for European security policy still have roots in the decisions and commitments of the powers involved in the process of German reunification thirty years ago? How did the Clinton administration come to support full Article 5 NATO enlargement rather than NATO’s Partnership for Peace? And what can we learn from those events to address the challenges of today?