In recent years, academic librarians’ roles have increasingly encompassed practices of knowledge production, spurred in part by their role in supporting the creation and dissemination of university research outputs. Shifts in institutional trends have also seen librarians’ widespread adoption of Twitter to share information and encourage collaboration. There is little research, however, about relationships between knowledge production in HE and librarians’ Twitter practices. The few existing studies about librarians and Twitter tend to trivialise such work as promotional. This thesis investigates the mundane work and practical politics animating academic librarians’ practices of knowledge production via Twitter. Guided by a theoretical framework about knowledge infrastructures that posits that designing and maintaining infrastructure has concomitant effects on knowledge production, this multi-sited ethnography was informed by six librarians from one UK research-intensive university. Empirical data was generated from two rounds of interviews, Twitter activity diaries, Twitter Analytics data, a focus group and written follow-up questions. Research outcomes suggest that as academic librarians negotiate the promises (i.e., the perceived potential or possibilities) of Twitter, they engage in practices of knowledge production. Four main practices of librarians implicated in their knowledge production via Twitter include justifying Twitter work as efforts to contest stereotypes of librarians (Invisibility); grounding Twitter work in modern interpretations of librarian’s ‘traditional’ values (Roots); managing the multiple scales and ambiguous engagement of Twitter (Scale); and troubling institutional hierarchies to foster scholarly community, whilst spurring new vocational identities for librarians (Culturality). By building a holistic picture of librarians’ practices, the thesis contributes insights into new and devolved practices of knowledge production in HE, thus complicating depictions of university professional groups in the scholarly literature. The study furthermore suggests that drawing attention to quiet areas of work in the university helps demonstrate the fragility and contingency of practices in HE considered static or unassailable.