Expert professional practice in any field is known to rely on both explicit (formal) and tacit (personal) forms of knowledge. Current anaesthetic training programmes appear to favour explicit knowledge and measurable competencies. We aimed to describe and explore the way different types of knowledge are learned and used in anaesthetic practice. Method. Qualitative approach using non-participant observation of, and semi-structured interviews with, anaesthetic staff in two English hospitals. Results. The development of expertise in anaesthesia rests on the ability to reconcile and interpret many sources of knowledge—clinical, social, electronic, and experiential—and formal theoretical learning. Experts have mastered technical skills but are also able to understand the dynamic and uncertain condition of the anaesthetized patient and respond to changes in it. This expertise is acquired by working with colleagues, and, importantly, by working independently, to develop personal routines. Routines mark the successful incorporation of new knowledge but also function as a defence against the inherent uncertainty of anaesthetic practice. The habits seen in experts’ routines are preferred ways of working chosen from a larger repertoire of techniques which can also be mobilized as changing circumstances demand. Conclusions. Opportunities for developing expertise are linked to the independent development of personal routines. Evidence-based approaches to professional practice may obscure the role played by the interpretation of knowledge. We suggest that the restriction of apprenticeship-style training threatens the acquisition of anaesthetic expertise as defined in this paper.