This article analyzes the main features of radical Islam in Spain and the role that Islamist radicalism plays in the radicalization of a significant minority of the Muslim population in Spain. It also examines the implications of the expansion of radical Islam on radicalization toward violence among segments of Spain's Muslim communities and on dynamics of social cohesion more broadly. The article argues that certain aspects of radical Islam strongly propel radicalization toward terrorism constituting early indicators of violent radicalization. The individuals on whom this ideology resonates and impact in a profound way are acutely vulnerable to violent radicalization.