This dissertation offers a bilingual analysis of the transnational co-formation of U.S. and Mexican cultural nationalisms in the 1920s and 1930s, and investigates the intra-hemispheric networks of modernist practice and exchange in the Americas. Drawing on a wide variety of materials (culturalist essays, poems, paintings, journals, etc.) from such diverse writers and artists such as Waldo Frank, Stuart Chase, John Dos Passos, Thomas Hart Benton, Alfonso Reyes, José Enrique Rodó, Diego Rivera, and Salvador Novo (among others), this project reconstructs the polydirectional process of cultural collaboration through which the gendered and racialized vocabulary of U.S. and Mexican nationality was produced, transacted, and sometimes contested. On the one hand, my focus on the circulation of goods, people and ideas investigates how the transnational movement of culture contributed to the reification of the language of cultural and/or national difference in the Americas. On the other hand, I argue that the traveling of culture generated forms of expression and identification that challenged the nationalist discourse of U.S. and Mexican sovereignty. Finally, this dissertation explores the unexamined relationship between Americanism and modernism, and considers the distinctive traits and shapes of modernist art in the Western Hemisphere.