The two years following 2014 were challenging for European security and for NATO. Russia's behaviour on the international scene changed the nature of the debate about the future of European relations with Moscow. At the same time, a new and dangerous threat known as the Islamic State arose in the deserts south of NATO. This chapter offers an introductory overview of NATO's adaptation measures in response to this changed security environment. Several modest initiatives were taken at the Wales Summit in September 2014 to deal with these challenges, but these measures were just a first step. The July 2016 Warsaw Summit agreed to a much tougher set of force goals that reflect a return to thinking about deterrence and making collective defence NATO's first priority. NATO's initial reaction to the events of 2014 was modest. Russia's foreign-policy behaviour in Crimea, in Ukraine, and in public statements attacking the Alliance, came as a shock to most member states.