This chapter investigates the relationship between radicalization and conversion. There are two main ways of envisioning the conceptual links between these notions. The first one, informed by some recent statistical evidence, argues that conversion provides fertile ground for radicalization and that converts are more likely than other believers to engage in the path of politico-religious violence. The second one, motivated by theoretical concerns, suggests that radicalization is best defined as a subtype of conversion (one that involves violent ideology and action), and that scholars working on radicalization have much to learn from the conversion and new religious movements (NRMs) literature. This chapter alternately explores these two options: It concludes that the first option tends to reproduce the shortcomings underlined by critiques of the radicalization concept and that the second one is most promising in terms of theoretical and empirical prospects.