This article makes the case for Posthumanist Institutional Ethnography (PIE). In doing so, it builds on and diverges from Dorothy E. Smith's post-structural work on Institutional Ethnography (IE), and speaks into recent discussions on the contested nature of ethnography. Drawing on the work of Donna Haraway, Karen Barad and Jane Bennet, and on empirical data from two recent projects, the article argues that PIE, in contesting human exceptionalism, places the human in relation to other-than-human objects, bodies and materialities, and thereby radically recasts ontology, epistemology, and ethics. Six features of PIE are identified. These features are put to work via an analysis of material moments which illuminate how gendered inequalities are produced, enacted and materialised in complex institutional ecologies. The article's theoretical and methodological contributions provide new insights into the fluid, ephemeral and affective materialisation of gendered politics in institutions.