How do everyday people-or actors who do not occupy positions of political authority-legitimate political systems? Responding to this question, I use work from sociology, political science, and cognitive science to build a theory of "Popular Political Legitimation" (PPL)-defined as everyday people's legitimation of a political system. To answer how PPL happens, we must To answer how PPL happens, we must answer two sub-questions: 1) What are the processes of socialization through which individuals learn the norms, widely held beliefs, and values that create the perception of consensus about compliance with political power? 2) How do individuals subsequently use these norms, widely held beliefs, and/or values to help reproduce the perception of a consensus about the compliance with said power through legitimation? In this light, then, we see that a model of socialization is central to understanding how PPL happens. Thus, to understand legitimation we must understand how individuals are socialized into norms, widely held beliefs, and values (sub-question 1) and then how said norms, beliefs, and values are used for PPL (sub-question 2). The goal of article is thus to develop a model of PPL that incorporates a model of socialization. This article will formulate a theory for answering the how question of PPL by addressing sub-questions 1 and 2. I develop this model in four steps. First, I review eight literatures from sociology, political science, and political psychology that address political legitimation, justification, and rationalization. The core gap in these overlapping literatures is that they lack a model of socialization that explains legitimation-although many of these literatures include socialization as a motive or factor for legitimation. Next, I review the literature on political socialization from sociology and political science and find that it also does not explain how socialization generates legitimation. Third, I turn to neuroscience and psychology (for reviews see Greene, 2017; Cushman, 2020) to review models of socialization and rationalization. Here, I pay special attention to "dual-process models." Finally, I synthesize these literature reviews to develop a dual-process model that explains the link between political socialization and PPL. In my review, I outline different literatures in order to showcase their nuances. Each literature makes important contributions that distinguish it from other literatures. The review section then celebrates these nuances and particularities as they relate to the concepts of PPL and socialization. The theory building section, then, synthesizes these accounts-thus building theory by highlighting the commonalities of these different literatures in order to create a single narrative about political socialization and PPL. Ultimately, I build a dual-process model that theorizes political socialization and incorporates an account of how Type II processes are used for PPL. It is important to note that dual-process models each have a specific application and thus scope c...