Many European countries have large and growing Muslim minorities. This is particularly true for the countries of Western Europe that have experienced influxes of Muslim immigrants over the last several decades from a variety of Middle Eastern, African, and Asian countries, as well as Turkey and the Balkans. Today, although some Muslims in Europe are recent immigrants, others are second-or third-generation Europeans. While expanding Muslim communities pose significant social and economic policy questions for European governments, the realization that some segments of Europe’s Muslim populations may be susceptible to radicalization and terrorist recruitment has also sparked security concerns in the decade since the September 11, 2001, terrorist attacks on the United States., The vast majority of Muslims in Europe are not involved in radical activities. However, events such as the 2004 and 2005 terrorist attacks in Madrid and London, respectively, that were carried out by Muslim citizens or residents, have raised the question of whether European countries have done enough to integrate their Muslim communities and prevent feelings of social exclusion and marginalization. Although not the sole cause of radicalization and terrorism, some experts believe that past failures to fully integrate Muslims into mainstream European society may make some Muslims in Europe more vulnerable to extremist ideologies., This report examines policies aimed at promoting integration, combating terrorism, and countering violent extremism in five European countries with significant Muslim populations: France, Germany, the Netherlands, Spain, and the United Kingdom. The report also evaluates the role of the 27-member European Union (EU) in shaping European laws and policies related to integration and counter-radicalization.