Latinos represent a large ethnic minority group in the United States, but their political participation, including on social media, is low compared to other groups. Guided by social identity and social cognitive theories, this study examines the influence of two dimensions of ingroup identification (i.e., group self-definition, group self-investment) on Latinos(as)' political expression about immigration and Latino culture on social media, the mediating role of pro-attitudinal selective exposure to media content related to these topics, and the moderating role of collective efficacy. Results suggest a positive and consistent association between group self-definition and social media political expression (SMPE) about both topics. Further, pro-attitudinal selective exposure was found to mediate the relationship between group self-definition and expression about both topics. Finally, collective efficacy moderated the relationship between group self-definition and SMPE about immigration.