Over the past decades, there has been an increase in English as a Medium of Instruction (EMI) programs in higher education. Nevertheless, the question remains whether EMI has a (negative) impact on academic achievement (e.g., test scores or course grades) in comparison to education in the mother tongue. In the current project, we will run several studies, using a variety of research methods, to investigate (a) the relation between education language and academic achievement, (b) the mediating role of cognitive processes (such as memory processes) and student factors (such as motivation and language proficiency) for this relation, and (c) the development of these student factors in EMI vs non-EMI education. To this purpose, we will run lab experiments of text studying under controlled circumstances, but also both a longitudinal and intervention study in real-life classrooms. Furthermore, we will run a big data analysis of a database containing thousands of records of student profiles (e.g., SES, motivation, language proficiency, former education, cognitive ability, etc.) and grades for EMI and non-EMI courses. This database will allow us to identify general trends in EMI vs non-EMI education, but also to further investigate specific student factors mediating the relation between education language and academic achievement. In all, these studies will contribute to both the theoretical and practical domain of EMI education.