Background: Work-based non-formal learning plays a key role in faculty development yet these processes are yet to be described in detail in medical education. Aim: This study sets out to illuminate these processes so that potential benefits for new and inexperienced medical educators and their mentors can be realised. Method: The non-formal learning processes of 12 novice teachers were investigated across hospital, general practice and medical school settings. The research sought to describe 'what' and 'how' non-formal learning takes place, and whether these processes differ across teaching sites. Both clinical and non-clinical teachers of medical undergraduates from one inner city medical school were recruited for the study. Through semi-structured interviews and a 'concept map', participants were asked to identify the people and tasks which they considered central to helping them become more expert as educators. Results: Results identified non-formal learning across a number of key dimensions, including personal development, task and role performance, and optimising clinical teaching. This learning takes place as an outcome of experience, observation, reflection and student feedback. Conclusion: Non-formal learning is a significant aspect of the development of novice teachers and as such it needs to be placed more firmly upon the agenda of faculty development.