"It is not easy to predict the future course of events, which will depend to a large extent on the overall political situation in the USSR" is the cautious evaluation of the confidential expert report for the North Atlantic Council in October 1989. In 1988-1991, the relationship was fundamentally transformed between the Western alliance system led by the United States and the East European socialist bloc dominated by the Soviet Union. The military, political, cultural, and ideological confrontation, with the weakening of Moscow and the collapse of its empire, was replaced during a few months by a new type of cooperation of the parties separated previously by the Iron Curtain. The eight reports from the NATO Archives (formerly classified confidential), published in the present volume for the first time in English, illuminate the East European events of these four eventful years from the perspective of expert advisors of the alliance. How were these dramatic changes in Eastern Europe perceived and interpreted in Brussels?