Russia’s aggression against Ukraine in 2022 has significantly changed the security situation in Europe, posing new challenges to NATO and forcing it to reconsider its strategic approaches to ensuring regional stability. The relevance of the topic is driven by the need to assess NATO’s role in deterring threats, strengthening its eastern flank, and developing cooperation with Ukraine as a key partner. The purpose of the study is to examine the transformation of NATO’s role in ensuring security in the region after the outbreak of a full-scale war in Ukraine. The study uses the methods of system analysis, content analysis, comparative analysis, and case studies to assess strategic decisions and their impact on regional security. It is established that after 2022, NATO returned to the priority of collective defense, which was reflected in the deployment of additional multinational battlegroups, strengthening of military infrastructure and expansion of exercises on the eastern flank. Deepening cooperation with Ukraine has gone beyond traditional aid to include joint planning, intelligence sharing, and enhanced cybersecurity. One of the key factors has been the integration of the experience of the Ukrainian Armed Forces into NATO standards, which contributes to the defence capabilities of the entire Alliance. The practical significance of the results obtained lies in the possibility of using them to develop Ukraine’s strategic documents on integration into the EuroAtlantic security system. Particular attention is paid to the issues of ensuring the resilience of critical infrastructure and responding to hybrid threats, which remains relevant for all Eastern European NATO partner countries.