Terrorist cells include "home-grown" and externally inspired groups. Contrary to popular belief, most terrorist incidents in Europe since September 11th have not been purely home-grown, but have drawn on sponsorship, support, or guidance from al Qaeda. Subversive networks use methods short of violence in order to further extremist objectives. Such methods include establishing front groups; penetrating and manipulating political parties; infiltrating the armed forces, police, and other institutions; and generating civil unrest through demonstrations, strikes, and boycotts. Subversive networks sometimes have terrorist links. The current threat is a political ideology that cloaks itself in religion, cynically exploiting religious tolerance in order to prevent democracies from acting against it. Extremist political movements have similar goals, but these groups use primarily peaceful political means. Insurgent sympathizer networks are informal groupings that often lack fixed structure. They function as clandestine underground networks with an innate capacity to threaten their host societies. They provide "strategic depth" to terrorist groups, who recruit from these networks to replenish losses and sustain operations. Crime and terrorism overlap in Europe to some extent. This occurs as those involved in narcotics, smuggling, people-trafficking, document fraud, and money laundering establish alliances of convenience with terrorists. Countersubversion efforts must aim to reduce the appeal and influence of subversive groups by countering motivations to become involved in these networks; countering their ideologies with normative, positive ideologies; countering efforts to find sanctuary in European societies; and countering specific activities of the subversive groups. 3 figures and 117 notes