This dissertation is a study of the relationship between the Alianza de Camioneros, the organization that represented Mexico's middle-class bus industry entrepreneurs, and the soft-authoritarian regime that governed the country from 1929 to under the Institutional Revolutionary Party (PRI). The PRI's 71-year rule defies easy explanation. Its legitimacy was shallow and uneven, yet it did not use outright repression to retain power. Rather, it relied on the coherence and loyalty of a broad group of mid-level elites who acted as intermediaries between the regime and society. Its mid-century dominance was possible because it retained the allegiance of those actors. Drawing on a range of official documents and private publications this dissertation explains how it did so. Through the biographies of Alianza leaders, I argue that the history of a priísta political culture prevented elite ruptures and thus lent crucial strength to soft authoritarian rule. This system included the unwritten rules that kept order on the political playing field and determined the terms of the relationship between intermediate elites like the Alianza's leaders and the regime. I trace the career of Antonio Díaz Lombardo, the Alianza's leader from 1929 until 1954 to offer a "long arc" perspective on the formation of the PRI regime and argue that the incorporation of entrepreneurial groups stabilized the postrevolutionary state in a process involving changes in political institutions and the development of a "political style." I follow José Valdovinos, the Alianza's leader from 1954 to 1958, arguing that the relationship between intermediate elites and the regime was renegotiated during the 1950s in response to public pressures. In examining Isidoro Rodríguez's struggles for power within the Alianza I reveal how the PRI's corporatist system maintained the loyalty of mid-level elites. Through the career of Rubén Figueroa, I demonstrate how calculations of "political strength" shaped the construction of clientelistic networks. Finally, through the experiences of the Alianza's last leader, Hector Hernández Casanova, during the municipalization of the urban bus system in 1981 I show that by the late 1970s the political culture that had supported mid-century stability was beginning to decay