In this chapter, we presents the results from a multi-method study in the Netherlands into the role of socio-economic and psychological factors underlying terrorism involvement. Building on theories and findings of previous researchers in the field, we present a descriptive model of terrorism that categorizes distal and proximal ‘threat triggers’. In the quantitative part of the study, we analysed a combined data set on suspects of terrorist offenses, a control sample of the general population and a sample of general offenders. Terrorism suspects were more often lower educated, unemployed, and previously involved in crime compared to persons from the general population with the same gender and age. Relatively often, they had lost their job or became imprisoned for another crime a year before they were charged with a terrorist offense. In the qualitative part of the study, we conducted interviews with four detainees from terrorist units, eight detainees charged with traditional crimes (as reference group), and 18 professional informants that had personal experience with current and former detainees on terrorism and other offenses. The results of these interviews suggest that among terrorist offenders, early family experiences, attachment problems, and mental health issues increase feelings of perceived threat, which further justify violent narratives of belonging and significance.