By examining how a student from Vietnam used English to interact with her peers in an English-medium secondary school in Singapore, this paper argues for an examination of language and literacy development through a cosmopolitan lens. Building on earlier research on cosmopolitanism (e.g., Campano & Ghiso, 2011; Canagarajah, 2013a, 2013b, 2013c; Hansen, 2010; Hull & Stornaiuolo, 2010), I illustrate how a broader understanding of cosmopolitanism in language and literacy education is timely in the wake of contemporary transcultural flows that characterize globalization, the emergence of a neoliberal order in education, and a pressing need to address educational inequities encountered by the growing number of immigrant learners whose home languages may not be valued in classrooms. The data in this paper, which include politicalspeeches, school documents, and classroom interactions, are part of a larger, yearlong critical ethnographic study and are subjected to microethnographic discourse analysis (Bloome & Carter, 2014). Through investigating how local interactional events are linked to broader events in wider Singapore society, I demonstrate how my Vietnamese focal student and her Singaporean peers were able to enact and develop a cosmopolitan outlook. Implications on language and literacy development are also discussed.