This paper focuses on peer learning as a process to develop PhD students' disciplinary and scholarly skills. PhD students' experience is not usually framed in terms of peer learning, because peer learning is more often studied and applied at the undergraduate level. This contribution builds on an ethnography of a research team to show the potential of peer learning over the course of the doctorate. A socio-constructivist conceptualisation of learning, inspired by activity theory, guides the analysis. The contribution of this paper is threefold. First, it proposes an original definition of learning that highlights process and practice, and shows how to work with it. Second, it demonstrates how peer learning unfolds in the interplay between structured and emergent types of interactions. Third, it provides scholars with insights into the conditions facilitating peer learning and stimulates debate around the initiatives that institutions can put in place to support PhD students.