The field of critical security studies has recently generated innovative research on processes of ‘securitization’ of immigrants and minority groups. Yet, much of this research has concentrated on the discursive aspects of ‘securitization;’ at the same time, the institutional mechanisms of securitization have not been subject to systematic research. My presentation explores comparatively the exclusion of Jews from citizenship rights in Romania and Serbia during the ‘long nineteenth century’ in order to underscore the intricate links between processes of securitization and discourses and practices of citizenship. During their protracted transition from Ottoman provinces to modern nation-states, these two nascent constitutional monarchies excluded Jews, for decades, from substantial civil and economic rights, full emancipation being achieved only under pressure from the Great Powers. Why were Jews excluded from citizenship rights? What were the legal and political techniques employed for their exclusion? I argue that the denaturalization of Jews was triggered by a process of “securitization,” which entailed the social construction of a “Jewish threat” to the ethnic majority’s collective “societal security,” and its institutionalization in practices of citizenship closure. The presentation underscores the nativist rhetorical strategies of mass mobilization as well as the institutional means by which anti-Semitic political entrepreneurs succeeded in implementing policies of (selective) citizenship closure. I identify several steps in this process of exclusion, which correspond to stages in the development of nation-states in the Balkans. Based on the findings of this case study, more general conclusions are derived about the historical interplay between practices of securitization of certain societal issues and the denaturalization of various categories of “unwanted citizens.” The presentation is part of a larger research project in progress on the emergence, evolution, and main features of nation-state citizenship in the modern Balkans.