The article is devoted to the crucial problem of modern international relations like NATO-enlargement to the East in the last 10 years. Firstly, the short pre-history of the NATO-transformation that brought to the non-stop enlargement is given, then the enlargement process is characterized both in military and political aspects. It is being explored from inside not only as geographical, but also as institutional enlargement and enlargement of missions. The article is focused on the changing role of NATO, which is reflected in the military actions of the alliance outside its juristic borders without taking the UN Security Council’s resolutions into consideration.