This chapter analyses the adaptation of Poland’s defence policy and armed forces to the rapidly changing security environment along NATO’s north-eastern flank. First, it examines the impact of a resurgent Russia on Poland’s security calculus, especially since Russia’s seizure of Crimea and the war in eastern Ukraine. Next, it addresses the evolution of Warsaw’s views on the relative utility of NATO and the European Union and its efforts to return NATO to its traditional territorial defence role. It then focuses on the modernization of Poland’s armed forces, with a special emphasis on doctrinal change, the reform of the command and control system, and the creation of the Territorial Defence units. It also reviews the t state of key hardware purchases as of mid-2017. The chapter concludes with an overall assessment of the level of capabilities and the readiness of the armed forces in the changing threat environment along NATO’s north-eastern flank.