"The September 11, 2001, terrorist attacks gave new momentum to European Union (EU) initiatives to combat terrorism and improve police, judicial, and intelligence cooperation among its 27 member states. Since the 2001 attacks, the EU has sought to speed up its efforts to harmonize national laws and bring down barriers among member states' law enforcement authorities so that information can be meaningfully shared and suspects apprehended expeditiously. Among other steps, the EU has established a common definition of terrorism and a common list of terrorist groups, an EU arrest warrant, enhanced tools to stem terrorist financing, and new measures to strengthen external EU border controls and improve aviation security. […] U.S. and EU officials have negotiated some revisions to the existing passenger name record (PNR) accord in an effort to assuage EP [European Parliament] concerns. Other issues that have led to periodic U.S.-EU tensions include terrorist detainee policies, differences in the U.S. and EU terrorist designation lists, and balancing border security with legitimate transatlantic travel and commerce. Congressional decisions related to improving border controls and transport security, in particular, may affect how future U.S.-EU cooperation evolves. In addition, given the European Parliament's growing influence in many of these policy areas, Members of Congress may be able to help shape Parliament's views and responses through ongoing contacts and the existing Transatlantic Legislators' Dialogue (TLD). This report examines the evolution of U.S.-EU counterterrorism cooperation and the ongoing challenges that may be of interest in the 112th Congress."
CRS Report for Congress, RS22030