Progress within the field of radicalisation is evident. Yet while research increasingly adopts a quantitative approach to studying radicalisation processes, there is no sound empirical evidence base on the risk and protective factors for violent extremism and much research is not fit for practice. Day-to-day risk assessment and management of individuals deemed to be a potential risk to national security forms a core component of counter-terrorism. Each phase of counter-terrorism risk assessment and management requires state-of-the-art science for the identification of putative risk and protective factors, and to understand how such factors are functionally linked to violent extremism. This thesis provides a unique contribution to these research endeavours in several important ways. First, in order to explain why individuals radicalise, we have to turn our focus towards those risk factors and underlying mechanisms, which explain why and how certain individuals come to develop extremist propensities. Thus, this thesis’ main aim is to study risk and protective factors for the development of violent extremist propensities. Second, terrorism studies is over-reliant on secondary data. By conducting two unique large-scale nationally representative general population surveys, this thesis contributes towards establishing a robust empirical knowledge base. These are one of the first such surveys conducted within the field of violent extremism research. Third, radicalisation trajectories and engagement in violent extremism are characterised by complex constellations of risk as well as protective factors. Risk factors for one risk specification may not equally apply to others and the conditional and contextual nature of various factors need to be taken into consideration, which necessitates more complex analyses of patterns of relationships. This thesis draws on a range of structural equation models, conditional mediation models and interaction analyses, which allow for a better understanding of the underlying mechanisms and complex configurations of various risk and protective factors. The analytical designs embedded throughout this thesis are some of the first to test such interactions in an empirical manner. Fourth, this thesis uses an integrative framework which examines not just risk but also protective factors for violent extremism and draws on a wide range of validated theories from different disciplines to strengthen the explanation of relationships between factors. By utilising models with several risk/protective factors, this thesis overcomes some of the 'problem of specificity', as it delivers plausible answers as to why the vast majority of individuals, who are experiencing particular conditions or grievances do not develop violent extremist intentions. Such research designs may be able to identify those factors that can inform prevention and intervention programs. Fifth, radicalisation is a complex and multifaceted process with diverse pathways and outcomes to it. This inherent complexity renders radicalisation, as a construct, difficult to operationalise. A key part of conducting quantitative research is the development of adequate and validated instruments. Thus, by developing and validating psychometrically sound instruments, this thesis contributes towards rigorous quantitative research on violent extremism. This thesis addresses these issues through a number of novel research designs. First, I conduct a systematic review and synthesise the existing evidence on quantitative risk and protective factors for different radicalisation outcomes. However, several gaps as well as conceptual and methodological issues are identified, which are addressed in the following chapters. Second, I conduct a German nationally representative survey on violent extremism, and I apply structural equation modeling to employ a conceptually integrated approach to studying the individual and environmental-level determinants of differential vulnerability to extremism. The findings demonstrate the profound effect of person-environment reciprocity and, thereby, highlight key individual, developmental and social mechanisms involved in the development of extremist propensities. Increasingly, we are witnessing a seeming convergence between belief in conspiracy theories and ideological extremes. However, there is a dearth of empirical research on the relationship between conspiracy beliefs and violent extremism. Therefore, third, this thesis conducts a unique quantitative analysis on this relationship and the findings highlight the contingent effects of risk and protective factors, which are defined as ‘interactive’ or ‘buffering’ protective factors. This has major implications in regard to prevention strategies of ‘at-risk’ populations. Fourth, based on a large-scale UK nationally representative survey, I develop and validate a novel psychometric tool to measure individuals’ misogynistic attitudes. Fifth, recent incidents have demonstrated that misogynistic beliefs can lead to acts of mass violence. This thesis provides the first survey-based study on the relationship between misogyny and violent extremism by examining the underlying mechanisms and contingent effects linking misogyny to (extremist) violence. Collectively, the dissertation’s results demonstrate that multiple factors likely contribute to individual pathways into violent extremism. No single risk or protective factor exists that can explain its genesis. This has significant implications for practice and policy. Preventing and countering violent extremism (P/CVE) programs must take account of the constellation of multiple factors that interact with (and sometimes enable or disable one another) rather than solely focusing upon single risk factors. These findings stress the need to implement evidenced based prevention and interventions programs, which have to address these risk factors early on, before they properly take hold and become so deeply ingrained that they are almost intractable. Therefore, increased focus of P/CVE interventions should be put on the indirect, long-term and life-course oriented protective factors.