In contradistinction to existing typologies of terrorist organizations by ideology or intent, a functional classification is suggested. By analyzing terrorist groups according to their target population and base of operation, 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. Whereas the struggle against foreign-based terrorists must focus on reducing the sponsoring countries' motivation to support them, the battlefield regarding domestic-based groups is home public opinion.