The use of English as a medium of instruction (EMI) has a long tradition in post-colonial contexts, the Nordic countries, as well as in Turkey and the Gulf States. In recent years, EMI has also been introduced in many other parts of the world, including Spain, Italy, Russia, Japan, and China. EMI refers to an approach to teaching disciplinary content in contexts where academic subjects—particularly at the tertiary level—have traditionally been taught in students’ mother tongue or dominant language, but are now delivered by content specialists through the medium of English. The adoption of EMI is based on the assumption that it facilitates the successful learning of both academic content and English. However, the implementation of EMI raises several important issues, including the nature of academic literacy, the role of English in mediating disciplinary knowledge, and the impact of EMI on both content teachers and learners. These issues will be explored, and insights will be presented into how EMI teachers adapt their pedagogical practices to meet the demands of EMI.