The French government recently announced a plan to « fight against radicalization », and a series of measures aimed at preventing the passage to violence. Although the term is not entirely new to the French political language, it marks a departure from an anti-terrorism policy justified mainly by a judicial approach and enforced in great part through administrative measures. France is thus moving closer to the Netherlands and the United Kingdom, who have developed such policies since the mid-2000s. Yet what is, exactly, the « fight against radicalization »? How can we explain this new approach of the French government? And what can we learn from a decade of experiences of these two European countries? This study shows that the concept of radicalization serves as an effective discourse to legitimize police action beyond its usual areas of competence, investing many areas of diversity management such as education, religion, and social policies. The study traces the diffusion of the discourse through European institutions and analyzes, through the notion of « policed multiculturalism », the effects of its legal, administrative and preventive forms.