What do we know about radicalization and radical groups? This thematic issue focuses on these questions and this introduction sketches the outlines of the subject. Many researchers studied this subject from different angles, using various research techniques and sources of information.

This article presents an overview of the main determinants of radicalization and terrorism. Experienced discrimination plays an important role, and can be seen as threatening. This could amplify the importance of ideology and religious convictions, and these both unify the group and direct the behavior of the group. Perceived threats also result in emphasizing group identity and increases the cohesiveness of the threatened group. This may lead to polarization between groups and radicalization. This radicalization is also affected by cognitions, such as perceived inequity and injustice, as well as emotions such as anger and contempt. In a later phase of radicalization group processes, such as groupthink, and support from the wider social group may further strengthen radicalization. Justification processes, like dehumanizing the opponent, are also likely to play a role. Finally, the transition from radicalization to terrorism is discussed.

Tore Bjørgo was one of the initiators to gather an international group of researchers to join forces casting light on the subject of counter-terrorism. Together with John Horgan he edited a volume Leaving Terrorism Behind. In this article he focuses on the push- and pull factors influencing the decision to dissent from terrorism. It also discusses the ways in which counter terrorism policies can influence these processes.

Accounts of radicalization and of social movements are often flawed by a static understanding of participation in radical networks. By analyzing the practices of the Salafi movement and its participants in reviving, establishing and nurturing a moral community of true believers I will explore how participation in this movement is sustained. I will show that by teaching young Muslims a particular lifestyle, exemplifying what it means to be a true believer, the Salafi movement tries to establish a position as the moral guardian of the Muslim community. For Muslim youth in this movement the activities are a means to evoke and nurture the experience of belonging and an essential practice for being part of the community of true believers.

In this article we deal with the role of government in encouraging the decline of radical movements. We use the survey of factors promoting decline reported by Demant et al. (2008a). This overview will be further developed regarding the factor ‘official policy strategies’ on the basis of certain concepts taken from discourse analysis, adapted to counterterrorism and deradicalization strategies by De Graaf in 2009. The question posed is: ‘Which “narrative” can the government tell to encourage the decline of radical groups?’ We will therefore not address the different practical measures in this field, but focus instead on the perception of these official measures by the radicals. We will illustrate this process by means of a case-study: the deradicalization of South Moluccan youths in the 1970s. We will furthermore draw some lines to deradicalization of Jihadist radicals after 2001, also in the Netherlands.

This article describes the value of the Global Terrorism Database (GTD) for the study of terrorist groups. The GTD helps to illustrate trajectories of violence of specific terrorist groups, helps to explore differences in terrorist violence between groups and between periods of time, and allows the testing of hypotheses concerning the origins and manifestations of terrorism. This article highlights the benefits of the GTD, using examples. The strengths of the GTD, but also opportunities for improvement are discussed.