The transatlantic security relationship has been at the heart of cooperation since the onset of the Cold War and has been the foundation on which the stability of Europe has been built. But the post-Cold War period has raised major challenges for transatlantic relations as well as new security threats, such as terrorism, organized crime and drug trafficking. These are fresh concerns in the sense that they have not been previously regarded as matters for US-European cooperation. Recent events such as the 1999 war in Kosovo, the European Union's decision to create a Rapid Reaction Force and the US policy of proceeding with a ballistic missile defence capability have all contributed to tensions in transatlantic relations. The transatlantic relationship has entered a new and highly uncertain period. This book looks at the three main facets of the transatlantic security relationship: the defense of Europe, global challenges, and new security threats.