Over the past twenty-five years Universities in Europe are increasingly fostering their internationalisation mission to respond to the current mobility trends and global competition. Teaching subjects through the medium of English (English Medium Instruction or EMI) is widely considered to be an essential tool in the internationalization policies of universities. However, the introduction of EMI in a university can be a problematic process which raises a series of questions and challenges in regard to the accreditation and training of teaching staff. What level of English should teachers have in order to teach their subjects through English at university? What methodological skills are involved in teaching through another language? How can teachers be trained for teaching through English?