Considering dramatic cases of terrorist acts, the question about its causes arises naturally. In a large number of cases, processes of radicalization play a vital role. These are the core of the current chapter. At first, we define the associated terms of radicalism, extremism, and terrorism and differentiate those from the phenomenon of radicalization. After that, we discuss causes of radicalization. On the one hand, we focus on single factors which may contribute to radicalization according to current research. These are person and context factors, like authoritarianism and social exclusion, as well as individual and group processes, like the need for significance or phenomena of group polarization. On the other hand, we present established models of radicalization like the theory-based staircase model and the empirically underpinned radicalization puzzle. The chapter closes with identifying research gaps and outlining an agenda for practice and politics.
