This short paper describes the use of infrastructural theory to interrogate data gathered for an ongoing study on the Twitter practices of academic librarians at one research-intensive university in the United Kingdom. In tandem with wider changes in networked technologies and ways of producing scholarship, academic librarians’ roles have shifted increasingly to knowledge production, particularly in the area of research support. A related shift has been academic librarians’ adoption of social media, particularly Twitter, to disseminate information and encourage community and collaboration. The few existing studies of librarians’ Twitter practices, however, frame such activity as service promotion, overlooking the relationship between technology and professional practice entwined and concomitant social effects in the university. The theoretical framework devised for this study was woven from research in anthropology and Science and Technology Studies about the nature of infrastructure. Instead of viewing infrastructure as separate and monolithic substrates supporting the circulation of goods and information, such theory posits infrastructure as relational and contingent, constituted of political decisions and having broad and co[1]constitutive social effects on knowledge, subjectivities and agencies (Jensen & Morita, 2017). The study’s theoretical framework particularly draws on the notion of knowledge infrastructures defined as “networks of people, artifacts, and institutions that generate, share, and maintain specific knowledge about the human and natural worlds” (Edwards, 2010). The framework therefore emphasises the invisible labour of infrastructure — often dubbed infrastructuring — and related socio-political practices of design and maintenance that embody promises for the future (Larkin, 2018). In this picture, infrastructure is fragile and contingent, shaped by its installed base, and remarkably complicated, unfixed and open to contestation. Based on preliminary findings, the study argues that academic librarians' Twitter practices constitute knowledge infrastructures in higher education. Using an infrastructural framework helped foreground the material conditions of librarians’ knowledge production in terms of entanglements of technology and professional values, shifts in professional subjectivities and performative effects within the university. A tentative implication for studies of technology and learning is that, by insisting that infrastructure and social activity are intertwined, learners and teachers are not framed in opposition to infrastructure and are thus better able to contest totalising narratives surrounding infrastructural learning technologies such as VLEs or MOOCs. In this picture, therefore, infrastructure is not simplistically background bulwark or sinister force. Appreciating the invisible labour involved in creating and sustaining infrastructure is therefore important for understanding contemporary learning contexts.