This chapter analyzes the issues which have shaped the security debate in Europe since the fall of the Berlin Wall. Since the end of the Cold War, scholars and practitioners engaged in European security have had to learn a completely new activity – the conceptualization and management of a Europe that is no longer formally divided. After 1989 all of this changed. The fall of the Berlin wall, the collapse of the Soviet Union and the ‘freeing’ of the east and central European states transformed Europe. After the fall of the Berlin wall, debate over future security within Europe was marked by a period of optimism amongst Western analysts and policymakers. In 1999 the long-running crisis in Kosovo came to a head with Western military action against Serbia and Montenegro in response to the Serbian ethnic cleansing of the Kosovan ethnic Albanian majority. The war in Kosovo was a landmark in European affairs.