This volume describes the conditions that favor the formation of coalitions between international terrorist organizations, and how they function within the changing international system. These theories are tested against empirical data on actual cooperation between European and Palestinian terrorist organizations from 1968 to 1990, and cooperation between European left-wing terrorist organizations (the phenomenon known as Euro-terrorism) from 1984 to 1988. These findings form the basis of a broader theory concerning cooperation and coalitions between organizations involved in international terrorism. Finally, an attempt is made to verify whether the new terrorist players driven, at least theoretically, by religious motivation, will imitate the behavior of the ideological or nationalist organizations, and to test whether the theories concerning cooperation and coalitions developed in this volume apply to the new reality.