This chapter investigates teachers' translanguaging practice in English-medium instruction classrooms at a Vietnamese university, drawing together teacher beliefs and practices in teaching English as an academic subject. Data collection comprised interview, classroom observation, and stimulated recall interview, the participants being two English teachers in classes of non-English-major students. The teachers' beliefs about the benefits of translanguaging were usually, but not always, consistent with their teaching practice, as observation indicated that the teachers used translanguaging for more functions than they previously thought. In particular, the teachers frequently and strategically translanguaged for content teaching, classroom management, and affective purposes. The teachers did not see English and Vietnamese as in opposition or even as requiring separation; on the contrary, they saw the flexible use of both languages as supportive for the teaching and learning process. This suggests that the promotion of English-only instruction schemes is not suitable in such an English as a foreign language (EFL) context. Additionally, there is a necessity for raising teachers' and policy makers' awareness of the advantages of translanguaging in EFL classrooms. As such, strategic translanguaging should be included in teacher training programs so that teachers will be able to make the most of this practice as a learning aid and a way of moving forward pedagogically with EMI.