Psychiatry, more than most medical specialties, must engage with undergraduate medical education to prevent the further marginalisation of mental health within medicine. There is an urgency to the need for psychiatrists and educationalists to communicate, and for psychiatrists to be aware of developments in educational theory. The idea of ‘threshold concepts’ is currently widely discussed by educationalists. Threshold concepts are described as areas of knowledge without which the learner cannot progress, and which, when grasped, lead to a transformation in the learner's perspective and understanding. Threshold concepts have been criticised on conceptual grounds, and there is a lack of clarity as to how to identify them empirically. While they may represent a fruitful approach to the task of engaging medical students in psychiatry teaching, it is suggested that further development of the idea is required before it could be usefully applied. However empirical studies in other disciplines suggest that there may be associated benefits to the teaching of the discipline from trying to identify threshold knowledge.