Terrorism, and the radicalization of terrorists in particular, has become a focus for academics and practitioners in recent years. However, the concept of radicalization has a variety of definitions and this is due in part to its relationship to other concepts with no clearly agreed definition, such as terrorism. Clarifying the intellectual background is important if the various trends in radicalization are to be properly understood. A clear picture of such trends is essential for the analysis of the radicalization process which will enable law enforcement agencies, academics and policymakers.