This article examines how Europe fits into the broader international campaign against terrorism. It argues that Europe is both a source and a target of terrorist activity, and faces threats including Al Qaeda-inspired terrorism, extremist political parties, insurgent sympathizer networks, subversive movements, and the overlap between crime and terrorism. The article argues that the primary threat is terrorist-linked subversion, which seeks to manipulate and exploit the sociological and ethnographic features of immigrant communities. Islamic theology is a strictly secondary factor, and a focus on Islam as such is likely to be an analytical dead-end. The article examines countersubversion as a conceptual framework for counterterrorism in Europe. The article concludes that an approach based on trusted networks and close collaboration with communities is most likely to succeed.