The four International Baccalaureate (IB) programmes provide an inquiry- and concept-driven approach to teaching and learning in primary and secondary schools around the world. This educational philosophy is often different to teachers' previous training and experience, yet little research has been done into how continuing professional development addresses the challenge of understanding and implementing the IB programmes. This phenomenological study explored the professional learning experiences of seven experienced IB Diploma Programme teachers working in different international schools. The findings provide a rich narrative of the teachers' lived experience to show that, while official IB workshops are helpful in developing understanding of certain aspects of the Diploma Programme, ongoing, job-embedded learning is also required for deep understanding and effective implementation of the IB educational philosophy. This study shows how the theory of social constructivism provides a foundation for exploring a range of formal and informal learning options for teachers and schools to develop individual and collective understanding and implementation of the IB educational philosophy.