The use of English to teach academic subjects raises many issues. Central is the notion of disciplinary literacy, and the role language plays in teaching and learning in a discipline. This article provides an introductory discussion of English medium instruction (EMI). It is organised around nine questions that readers need to know about EMI: (1) What are the reasons for adopting EMI?; (2) What is the nature of EMI?; (3) What are the language demands of teaching in EMI?; (4) What are teachers’ views of their primary role and responsibility in EMI?; (5) What are teachers’ views of their primary role and responsibility in EMI?; (6) What is the impact of EMI on the teacher?; (7) What is the EMI teacher professional identity?; (8) What is the EMI learner?; and (9) How can students be helped to develop academic literacy? The impact of EMI on teachers’ ability to present content in depth is reviewed, as well as its impact on their sense of professional expertise.