<P><I>Radicalisation</I> is a conceptual investigation within Western liberal democratic societies that follows an analytical framework linking expertise theory to discourse analysis of publications from the academic, governmental, and non-governmental spheres, as well as a dozen interviews with experts in the field.</P><P>The reader will come to understand the socio-political configurations that led to the emergence of radicalisation as an object of study. The book also identifies the historical tensions regarding models, definitions, and operationalisation of the concept of radicalisation in social sciences research. Finally, a new model explaining how the term radicalisation became the central conceptual framework of a new field of expertise will be proposed. The book is situated within the fields of security studies, crime prevention, and sociology of expertise. The book is innovative in its distinct focus on the term radicalisation and the expertise thereof. With its diachronic an