This paper employs a socio-technical perspective to explore the role of complex work support systems in organising knowledge and providing opportunities for learning in professional work. Drawing on concepts from infrastructure studies, such systems are seen as work infrastructures which connect information, knowledge, standards and work procedures across sites. Professional work is correspondingly understood as an infrastructuring practice in which technologies, people and processes come together and make up the working relations that are necessary to perform work. Empirically, we focus on audit work with an audit support system called Descartes. We explore how social and material aspects come together in the formation of professional awareness and task accomplishment. The analysis shows how infrastructures may become visible and be acted upon not only in moments of breakdowns or innovation, as previous research suggests, but when uncertainty needs to be resolved and when an epistemic or analytic activity occurs. We argue that the notion of infrastructuring practice is useful for exploring work-based learning in technology-rich environments, in ways that not only point to issues of control and accountability but also to opportunities for epistemic engagement. (Contains 1 note and 2 figures.)