The role of local actors in negotiating and shaping policy processes has increasingly been recognised in the field of language policy and planning (LPP). Research into English-medium instruction (EMI) policy has also started to shift focus to classroom-level policy actors, particularly teachers. In the context of higher education in Asian countries, where EMI is still in its infancy, research has reported a mismatch between top-down EMI policy and its implementation (e.g. Tri & Moskovsky, 2019). While studies on EMI have explored teachers’ perspectives, little is yet known about their actual classroom practices nor how these are shaped by contextual factors, both of which can demonstrate their agentive power in shaping EMI policy.

This study adopts an ethnography-based approach to explore how teachers exercise their agency in interpreting and appropriating EMI policy in Vietnam, where research output on EMI has not matched its phenomenal growth. Teacher agency here is investigated from an ecological perspective (Liddicoat, 2018), foregrounding teachers’ agentic capacity and their relations to governmental and institutional policy, other stakeholders, and even teaching tools. The study comprises case studies of three teachers in a Computer Science EMI programme at a Vietnamese university. Data collection involved in-depth interviews with the teachers, curriculum and lesson plan documents, multiple classroom observations over four months, and student interviews. Data were analysed thematically.

Findings reveal striking differences in the teachers’ professional histories, identities, and beliefs about the value of English, which shaped their EMI teaching practices and impacted student experiences and motivation. The teachers implemented different language policies in their classes, including “English-only”, bilingual or predominantly Vietnamese-speaking classes. The study highlights the role of teacher agency in appropriating EMI policy and the complex factors behind their decisions and actions in this context. It thus contributes to theorising micro-level stakeholders’ agency in LPP implementation and success.