Paul Hager and David Beckett have written one of the most important investigations into professional learning in recent times. The emergence of complexity: Rethinking education as a social science is a mature treatise that seeks to bring together practice theory and complexity theory, in the process advancing the concept of ‘co-present groups’ to ground their new way of thinking about learning. Throughout the long and often abstract argument, illustrations taken from previous studies by the authors and examples from writers pursuing related topics help readers to appreciate that here is a refined as well as penetrating analysis of contemporary problems in professional education, learning and development.