At the beginning of the 21st century it has become increasingly evident that the transatlantic relationship, which had been held together by the Soviet threat for almost five decades, is charac-terized by dissent rather than harmony. Tensions in the post-Cold War era eventually reached a climax in the run-up to the intervention in Iraq, when France and Germany opposed to join forces with the coalition of the willing, and Donald Rumsfeld coined the division between old and new Europe. Focusing on the combat against terrorism, the non-proliferation of nuclear weapons, and crisis prevention, this anthology addresses three fields of security and defense policy which have had a considerable impact on the relationship between the USA and Europe. The authors of this anthology analyze US and European perspectives on threats and the development of respective countermeasures. In addition to these fundamental aspects, the analysis also covers contemporary challenges such as the Iranian nuclear program and their impact on US-European relations.