This chapter considers researching English Medium Instruction (EMI) mathematics teaching and learning, drawing on our case study of mathematics lessons in a government secondary school in rural Rwanda. Conceptualising language and pedagogy as intertwined, agentive, socio-cultural and situated phenomena enabled us to examine how the teacher’s purposeful pedagogical approach, including his systematic and flexible use of a multilingual and multimodal semiotic repertoire, provided students access to English and mathematics. At the same time, we identify how subtractive EMI policy constrained student verbal participation, undermined teacher and student confidence in students’ language ability, and the extent to which the teacher described his pedagogy. We discuss our findings in relation to previous studies and highlight the need for further research. We recommend researchers engage teachers and policymakers with research-based insights in relation to their values, beliefs, and contexts to inform the development of locally relevant pedagogies and policies.