Professionalism is a core element of curricula in many disciplines but can be difficult to teach and learn.. This study used audio-diary methodology to identify professionalism threshold concepts in a small group learning setting in undergraduate medicine and to understand factors that might facilitate students to 'get' such concepts. 15 students and 7 tutors kept audio diaries over two terms. Data were analysed qualitatively for content. The key themes were then cross referenced to threshold concept criteria (for example where language indicated that learning was troublesome, integrative or transformative). Seven potential threshold concepts were identified which centred on students' developing professional identities including working with uncertainty, considering the bigger picture, not needing to know everything and professional culture. Reflection on workplace experiences within a small group helped students 'get' these concepts. The study concludes that threshold concepts and audio-diaries are useful tools for understanding lived experiences of professionalism learning. 3 complex and contextual nature of professionalism learning is increasingly being recognised, as is its potential as a transformational, life changing process rather than simply involving the acquisition of knowledge and skills (Wilson et al. 2013). Recent literature suggests that meaningful professionalism learning and professional identity development can be fostered by authentic experiences in and around the workplace (Reich, Rooney, and Boud 2015, Wilson et al.2013) and by providing opportunities for guided, critical reflection on such experiences (Mann 2009; Webster-Wright 2009; Trede, Macklin, and Bridges 2012). Moreover, where curricula provide opportunities for students to reflect on experiences which challenge or disrupt their worldviews and to share and to discuss their reflections with peers, this can lead to "more powerful and generative understandings" (Ryan and Carmichael 2015). Coherence, the ability to link theory and practice and see the practical relevance of learning, particularly when developed through interactions with peers and teachers, can be key to fostering students' identification with their profession (Heggen and Terum 2013). One way curricula can achieve many of the goals above is through facilitated small group learning, where students reflect on their experiences with peers, are encouraged to consider issues from multiple perspectives and challenged to consider things more deeply (Platzer 2000; Kahn 2013). This can result in more sophisticated and embodied understandings of professionalism (Monrouxe, Rees, and Hu 2011). Yet exactly how small group learning impacts on students' professionalism development and identity is under-researched; we know very little about students' lived experiences of such learning, including which professionalism concepts are troublesome and transformative and which elements of the small group setting facilitate shifts in student understandings. Threshold concepts There is growing int...