Abstract: The article presents the evolution of NATO's identity from 1991 to 2024, taking into account the perspective of the countries comprising the so-called Eastern Flank of NATO. Material and methods: The issues were identified and described based on a critical analysis of literature, reports, and official NATO strategic documents. Results: Demonstrating the implications for the security of the Eastern Flank NATO states arising from the post-Cold War transformation of the North Atlantic Alliance. Conclusions: In the 1990s, NATO began a transformation process. In addition to collective defense, its activities included conducting crisis response missions beyond the treaty area and fostering international cooperation. In the face of the Russian Federation's aggressive policies, the Alliance has once again prioritized collective defense and deterrence. The return to the Alliance's traditional functions is viewed positively in the Eastern Flank NATO countries; however, this has not resulted in a significant increase in allied military presence in these states.