This volume deals with a crucial, but underestimated, dimension of English-medium instruction (EMI) in higher education, namely the students' language experience and the improvement in English proficiency, the latter being one of the key motivating factors to opt for EMI. The mixed-method case study presented in this volume is a longitudinal investigation of the participants' language progress, spanning over two academic years. Although English language outcomes are neither mentioned in the definitions of EMI nor in the courses' syllabi, indeed, the EMI experience provides a large amount of language input for students, which is both assimilated consciously and partly as a result of incidental language learning. On reviewing previous literature on EMI, this book addresses some key questions such as the impact of EMI on the students' English skills, the increase of proficiency while focused on subject-oriented activities and in particular whether English improvement is voluntary or incidental. The data retrieved from questionnaires and language tests administered to one-hundred medical students enrolled in an Italian university provide valuable insights into the language factor in EMI, which may be usefully exploited and extended to other higher educational contexts. This book will be of interest to scholars, teachers and students investigating the internationalization of higher education and the impact of EMI on students' English proficiency.