This paper reports on a study of how liminality relates to the facilitation of reflective practice in professional education. Liminality refers to sites and positions that exhibit 'in-betweenness', or bordering positions, that might draw together different institutional conditions. The present project aims to examine the role of liminality in professional educational practice with a specific focus upon how liminality may support student reflection. Using a qualitative and comparative research approach, we analysed interview and observational data from police education and a medical programme. Observations and interviews explore practices of collective interactional (and hence observable) reflection at sites that are characterised by 'betweenness' of work and education. Findings indicate that situations that afford reflection are characterised by a sense of "undeterminedness" in terms of either the subject, space or activity. Thus, we conclude that there is some evidence that liminality affords reflection, but also that liminality and underminedness are fragile states that are not easily organised in a professional education curriculum.