How does a city become a city? This dissertation offers an answer by explaining São Paulo’s rapid transition from village to metropolis. More precisely, it examines the Brazilian city’s theaters between 1854 and 1924 to elucidate how Paulistanos adapted to their nascent mass society. As hundreds of thousands of immigrants and migrants poured into São Paulo, residents from across the social spectrum turned to theaters for entertainment, community, and social uplift. It was inside São Paulo’s theaters, the dissertation argues, that different groups began to articulate and realize their own vision for an urban public, that is, a social body fit for the crowds and visibility of city life. To understand what this social body entailed, I analyze three groups of theater producers: government officials, associational leaders, and businessmen. I show that, while no single notion of an urban public spanned all of the producers examined, most agreed on the need for the orderly juxtaposition of individuals through a shared understanding of “culture.” Theaters in this manner offered Paulistanos the possibility of rethinking social transformation: not only could culture be learned by all Paulistanos, meaning that men and women of every age and background took part in the urban public, but it could also be learned and defined outside the church and home. In other words, by taking advantage of São Paulo’s minimally regulated growth to erect their own mass spaces, theater producers situated social transformation in the secular public arena and within reach of most Paulistanos. In explaining the mechanisms by which theater producers did so, this dissertation illuminates how Paulistanos shaped on a mass scale the social categories and norms of the inchoate metropolis.