Despite junior doctors having an occupational preparation that includes extensive practice-based experiences, they often struggle to effectively transition to clinical practice. In particular, junior doctors often lack the competence and confidence to prescribe safely and effectively in the clinical setting. This chapter focuses on the development of specific medical knowledge through a consideration of co-working: a learning process comprising engagement with more informed partners. It specifically discusses how junior doctors can engage with pharmacists to develop prescribing skills. It draws on interviews with junior doctors, consultants and pharmacists about co-working arrangements and how they support doctors’ transitions to safe clinical practice. As pharmacists sit outside medical teams, an additional consideration is how specialist, but non-medical health care workers, can effectively assist this transition.