This article studies the transformation of the debate about national culture in twentieth-century Mexico by looking at the complex relationship between discourses of authenticity and mestizaje. The article firstly demonstrates how in the first half of the twentieth century, Mexican national identity was constructed out of a state-led program of mestizaje, thereby supposedly giving rise to a new and authentic identity, the mestizo (nation). Secondly, it is argued that the authentication project around mestizaje is riddled with paradoxes that require explanation. Thirdly, the article studies the political dimension of the authenticity discourse and demonstrates how the homogenizing and unifying forces that spring from the process of authentication played an important role in buttressing an authoritarian regime. Fourthly, the article looks at two recent developments: indigenous cultural politics and transnationalism. Here it is shown how discourses of difference, pluralism, and transnationalism are challenging the central tenets of Mexican post-revolutionary national culture and the boundaries of the national Self.