This thesis examines the question of the conversion of certain young French people to the radical version of Islam. As a matter of fact, the expression of « radical conversion » concerns the radicalization of attitudes, postures, looks, visions, representations, thoughts, etc., or in a word ideological perspectives. That is to say, it is by no means a question of young people who have taken on terrorist or radical acts but who display radical attitudes (rupture with the world, religious rigor, ideological, politico-social activism, etc.). For us, it is a matter of questioning the subjective and objective springs of this phenomenon by trying to answer the main question, namely how do these young people convert to radical Islam? We therefore put forward two hypotheses: first, the conversion to radical Islam is a social construction by stigmatization in other words, society organizes the conversion by a labeling process leading individual to be part of a primary social deviance prolonged in a secondary religious deviance. Then, radicalization Radicalisation or Radicalization is the process by which an individual or a group comes to adopt increasingly radical points of view in opposition to a political, social ou religious réality. Multiple pathways can promote the process of radicalization. This process starts with meaning searching effort to a crisis before being involved in radical groups. In other words, radicalization, like the phenomena of dependency or addiction (alcoholism, Tobacco and drugs, etc.) operates in a process leading the individual to become part of social deviance. To test these hypotheses, we rely on a constructivist approach by putting forward the notion of socialization and on the interactionist paradigm by mobilizing the notions of « deviant career, moral career, labeling and stigmatization » to finally arrive at formulating our expression of « radical career ». For the methodological aspect, we rely on the qualitative methodology based on two complementary techniques : the semi-directive interview of the biographical type and the participant observation (ethnographic). In this sense, the anchored theory revolving around a back and forth between theory and the field makes it possible to verify the validity of our theory framework and the frameworks: conceptual and theoretical mobilized. Between a search for meaning, an existential void, a religious rigor, an exaltation of the radical group, a dehumanization of others, a disempathy, a shaping of the body, an existential hapax, a revelation or a divine light, etc., conversion takes various interpretations, often subjective. These finally lead us to identify the phases or séquences of the process ranging from a quest for meaning, to a radical career through an existential crisis, an apprenticeship in radicalism and its maintenance, an eclipse of the subject, an objectization and a dehumanization. of others.