This article seeks to determine the main predictors of political participation in a newly democratic regime: Mexico. Compared to other nations, Mexico fills a moderate position in terms of the volume of political participation. Following the literature on participation, this study develops a set of participant modes—voting, communal activity, petitioning, direct action, and political organization membership—and then seeks to determine the socioeconomic, demographic, attitudinal, and social capital factors that best explain participation. Distinct resource inequalities limit the participation of the less educated, the poor, women, and workers, although peasant participation is robust. The strongest determinant of political participation of all kinds is involvement in social capital–generating activities: belonging to nonpolitical organizations and engaging in charitable work, activities typically dominated by the middle class. Building social capital is essential to promoting robust rates of political participation in Mexico.