This essay conceptualizes radicalization as a collective process that evolves within the context of global, national, or local intergroup tensions. People do not radicalize on their own, but as part of a group in which a collective identity is developed. Some members of the group may take a radical activist route to promote or prevent social change. Their interactions with their opponents intensify, while their ideas and beliefs sharpen. In this essay, I propose an interpretative framework to analyze radicalizing collective identities. The framework departs from the notion that supranational processes shape and mold the micro level of (radicalizing) citizens' demands, the meso level of social movements and political parties, and the macro level of national political systems. The answer to questions such as who radicalizes, why people radicalize, and the forms radical action takes lies in the interaction of supranational processes, national political processes, and the context of political mobilization. It is argued that radicalizing identities are key in this process, no radicalization without identification!