Political values represent a fundamental puzzle to the field of political science: Although they often contradict citizens' self-interest, citizens lean heavily on their values when making political decisions. I argue that, to better understand the puzzling nature of values, we must better understand value development at the individual level. In this dissertation, I put forward a new theory of value socialization, Social-Emotional Influence Theory, which posits that subjective group identification and emotion together imbue citizens with a sense of commitment to the values that dominate within their respective social identity groups. More specifically, I argue that group identifiers feel the "self-conscious emotions" pride, embarrassment, and shame in response to peers' positive and negative judgments of them and that these emotions push citizens in the direction of value conformity. In other words, when citizens identify with a group, they care what these peers think of them, opening them up to group influence. I test Social Emotional Influence Theory with data from several original experiments as well as a national Pew Research Center survey. Data from the Pew survey verify that Americans' politically relevant values vary according to social group and suggest that this variance is due to social conformity within groups. Three experiments then test whether social-emotional influence occurs among Catholics, college students, and Americans in general with respect to social conservatism, economic individualism, and economic equality, respectively. Overall, the data support the hypotheses that subjective group identification plays a key role in social influence over values and related attitudes and that pride, shame, and embarrassment mediate this effect of identity. I conclude by discussing future avenues of inquiry that would enrich our understanding of social-emotional influence as well as by discussing some of the normative implications of the proposed theory.