In 1995, six years after the fall of the Berlin Wall, NATO, a collective defence organization, Approved a very controversial document: the NATO enlargement report. Since then, the Atlantic Alliance has carried out four waves of enlargement into what was formerly called Eastern Europe. We can already assert that most of the members of the Warsaw Pact are now active members of NATO. Whereas it is true that this enlargement is based on defence motivations, this policy of the Atlantic Alliance is creating a security dilemma for Moscow. The aim of this work is, therefore, to prove that the waves of NATO enlargement have Affected the Russian perception of its national security. In this sense, I will analyse a number of Russian security documents, including its security and nuclear doctrine.