Radicalisation has become a central concept in contemporary security studies, aiming to understand the process by which individuals adopt extremist ideologies or engage in extremist actions. The term has shaped international counterterrorism approaches and strategies aimed at preventing political violence. Nevertheless, it remains contested due to scholars' critiques of its utilisation, such as the conceptual ambiguity, securitisation impacts, or methodological weaknesses. To address the major challenges in radicalisation research, this chapter presents authors' contribution to this edited volume. By exploring the history, theories, concepts, and current practices within this field, this collection aims to provide a comprehensive analysis of the subject. We believe that the volume will enhance scholarly debates and provide meaningful insights for researchers, policymakers, and practitioners working in the prevention of political violence.