Introduction In the previous chapter, we have reviewed various processes with the potential to foster radicalization and violence, amongst them group polarization, the dynamics of leadership, social support and, finally, a number of ways of justifying violence. All can help perpetuate radical solutions and accelerate the transition to terrorism. In the present chapter, we describe another factor of particular relevance to that latter process, the use of violent means: group performance or success and failure of the group. We also look at a small number of studies that have taken a different route, that is, comparing violent and non-violent groups on a number of characteristics in order to gain a better understanding of the whys and wherefores of radicalization and terrorism. Next, we will present a comparative analysis of certain selected groups, some of which did eventually take up arms and some of which did not. After all, as already stated in the introduction, not every radical movement makes the transition to terrorism; they may well find other means to achieve their goals. But when there seems to be no other way, violent action can represent the final phase in a process of radicalization. Next we will turn to research on how terrorism ends. What factors determine the end of a terrorist movement? What factors make people leave terrorist movements? Finally, we will turn to prevention and de-radicalization. What factors can help to prevent radicalization and are there programmes that can prevent further radicalization or help people to de-radicalize?