This article introduces a thematic issue of Transcultural Psychiatry with selected papers from the McGill Advanced Study Institute in Cultural Psychiatry on "Pluralism and Polarization: Cultural Contexts and Dynamics of Radicalization," which took place June 20-22, 2017. The ASI brought together an interdisciplinary group scholars to consider the role of social dynamics, cultural contexts and psychopathology in radicalization to violent extremism. Papers addressed four broad topics: (1) current meanings and uses of the term radicalization; (2) personal and social determinants of violent radicalization, including individual psychology, interpersonal dynamics, and wider social-historical, community and network processes; (3) social and cultural contexts and trajectories of radicalization including the impact of structural and historical forces associated with colonization and globalization as well as contemporary political, economic and security issues faced by youth and disaffected groups; and (4) approaches to community prevention and clinical intervention to reduce the risk of violent radicalization. In this introductory essay, we revisit these themes, define key terms, and outline some of the theoretical and empirical insights in the contributions to this issue. Efforts to prevent violent radicalization face challenges because social media and the Internet allow the rapid spread of polarizing images and ideas. The escalation of security measures and policies also serves to confirm the worldview of conspiracy theory adherents. In addition to addressing the structural inequities that fuel feelings of anger and resentment, we need to promote solidarity among diverse communities by building a pluralistic civil society that offers a meaningful alternative to the violent rhetorics of us and them.