This article offers a decolonial reading of professional development for English-medium instruction (EMI). The article zooms into the context of Taiwan, where the promotion of EMI has intensified since the 2030 Bilingual Policy was introduced. It is unclear, however, what constitutes EMI professional development, and to what extent the conceptualizations of EMI in existing courses and programmes improve or exacerbate colonial divides. By drawing on literature that look into the intersections of language, education, and de/coloniality, this article explores what a decolonial lens can tell us about professional development for EMI, and how this lens may provide new ways to rethink and remake it. From a website analysis of 66 Taiwanese universities that have received government funding under the Bilingual Policy, 15 professional development courses and programmes were identified and closely examined. The findings highlight three themes related to language, pedagogy, and context. To better support EMI faculty, this article argues that contextual questions should be foregrounded as they afford alternative perspectives in understanding the construction and communication of knowledge in teaching. Specifically, directing the focus to context means to acknowledge existing multilingualisms in EMI settings, and to work towards opening up spaces for linguistic, pedagogic, and epistemic diversity.