Essentially what I will do is to analyze from a comparative perspective the social support of three terrorist/ guerrilla movements: The IRA, the ETA and the HESBOLLAH. I will use the concept of the radical community to show that under certain circumstances segments of the population in question are transforming themselves into traditional communities which develop a solidarity with the terrorists which it is very difficult do break up by force. The paper will study the conditions under which this kind of transformation is likely to occur, the specific traits of the radical communities and their relationship to the violent groups, and finally the up and downs of this relationship in time. A final section will treat the question what is to be done with this kind of tightly fixed unions between the terrorists and their social backing.