This paper investigates the sources of mentors’ knowledge about teaching. The findings reveal that mentors’ knowledge about teaching is practice orientated and emerges from their professional experiences, their teaching skills, their pre-service teacher education and from their own personal experiences. The authors suggest that mentors require support to reflect on their early socialisation experiences and their attachment to practice-based experience as a source of professional knowledge, in this way they can better understand and carry out their role as mentors.