The number of universities offering English-medium instruction (EMI) is growing in Japan. Yet, academic programmes taught in English have not reached their full potential. One powerful barrier to the improvement of these programmes is a misperception that English language proficiency is the defining factor for success. After outlining the growth of EMI in Japan, this article considers the central challenge of faculty engagement as a key factor governing the development and sustainability of internationalisation activities. Problems involving the conceptual conflation of EMI and English learning and debates regarding English proficiency for EMI programme success are discussed. Interview data from faculty members involved in three Japanese university programmes demonstrates a foregrounding of the role of the English language and English proficiency is overly attributed as a barrier to programme excellence. Specifically, these misperceptions impede faculty engagement and prevent the implementation of quality faculty development efforts. This article proposes that less emphasis on language and greater attention to pedagogical and intercultural skills development could benefit EMI in Japan.