This study examines the alleged assurances made to Moscow during German unification discussions in 1989-1990. Specifically, Moscow alleges that Western governments offered assurances to the Soviet Union that NATO would not expand beyond its then current borders if Moscow agreed to allow a unified Germany to join NATO as a full member. Since the first post-Cold War round of NATO expansion in 1997-1999, Moscow has raised the issue of broken promises made to the Soviet Union several times. While it can be argued that the Soviet Union had little choice but to yield to Western pressures, it appears that in 1990 some U.S. and West German officials gave informal assurances with respect to Soviet security concerns, including potential NATO expansion eastward. This thesis examines the hypothesis that the United States, the Federal Republic of Germany, and other NATO countries did not make - and did not intend to make - a commitment ruling out future NATO enlargement, but that Soviet officials got the mistaken impression that such a commitment was made. The study investigates whether this hypothesis is supported by the evidence and considers how the Soviets received this impression. The study also discusses the implications of these misunderstandings for NATO-Russia relations.