After a brief discussion of the increasing importance of English in the lives of German university students, this article focuses on how the use of English as a non-native language in university lectures and seminars may affect the structure of these communicative events and their potential for the acquisition of knowledge. An analysis of empirical data from courses in Economics, Political Sciences and Chemistry (questionnaires and discourse data) provides some insights into students’ perceptions of the problems and benefits of English-medium instruction as well as into the strategies that students and lecturers use to support comprehension and to negotiate meaning while using English as a lingua franca for teaching and learning at a German university.