The purpose of this research is to analyze the main areas of reform that NATO has embraced during the last years, in order to assess its current position in the European security architecture and its prospects for the future. Almost overnight NATO's agenda changed drastically, including its plans formulated at the Wales Summit in 2014. NATO needed to focus on collective defense and find the answer on how to react to Russia's aggression and hybrid warfare model. NATO's traditional preparation for collective defense and its Article 5 commitments are facing nowadays significant challenge in Russia's approach to conflict, which combines many well-known elements with modern concepts and capabilities in a holistic, multidimensional and flexible approach that targets perceived weakness of the Alliance.