In the past decade, Japan has seen notable growth in English as a Medium of Instruction (EMI) courses in its universities (Bradford, 2018). While some EMI classes contain only domestic L1 Japanese students, others also contain international students. Discussions that take place in the latter context can be considered as English as a lingua franca (ELF) interactions (see Murata, 2018). This paper reports on a mixed-methods investigation conducted at a public university in Japan into how students feel about, and how they perform in, ELF discussion tasks in EMI classes. Questionnaire responses were collected from both 1st year domestic (n=48) and international exchange students (n=8). In addition, video recordings were made of groups performing ELF discussion tasks. Each group contained both English as a native language (ENL) speakers and L1 Japanese students. The questionnaire data indicated that despite some anxieties, both domestic and international students had a desire to communicate using ELF. A conversation analysis-informed examination of the interaction data showed that ENL speakers often dominated the discussions both in terms of language produced and the control they assumed over the task proceedings. However, there was also evidence of accommodation strategies used by the ENL speakers to aid communication (as also reported by Carey, 2010). The presenter will invite discussion of these points and their implications for EMI classes in Japan.