Four basic types of organizations are delineated: domestic-based xenofighters, foreign-based xenofighters, domestic-based homofighters, and foreign-based homofighters. On the basis of the operational objectives and specific limitations of these types of terrorist groups, it is proposed that xenofighters tend to adopt more indiscriminate tactics than homofighters, and that foreign-based groups tend to perpetrate international terrorism and are dependent on foreign countries' support. Countermeasures against domestic terrorists, who are dependent on local population support, essentially become a struggle for domestic public opinion. Denying foreign-based terrorists their base of operations can be achieved by varied means, ranging from subtle threats to the selective use of force. For example, the United States-Cuban agreement on the extradition of hijackers was an attempt to reduce each side's commitment to international terrorism. Finally, the most important factor in a country's willingness to cooperate with others in counterterrorist measures seems to be the extent to which that country itself is a target for terrorist attacks. One table and 9 references are provided.