The notion of 'professional practice knowledge' has been significant in some recent explorations of the nature of practice and discussions of the development of practitioners and practices. This article begins by outlining 'professional practice knowledge' as a window into practice, but suggests that practice has features that cannot be understood just from the perspective of knowledge 'in the heads' of individual practitioners. It suggests that practice has a number of extra-individual features that need to be elucidated. These include such features as being formed and conducted in social settings, shaped by discourses, and being dramaturgical and practical in character. Taking these into account yields a richer view of practice, and makes it possible to understand more readily why changing practice is not just a matter for practitioners alone, but a task of changing such things as the discourses in which practices are constructed and the social relationships which constitute practice. The article then offers suggestions about how changing practices might occur through public discourse among different kinds of people associated with particular practices (not just professionals alone), drawing on some of Habermas's insights into the nature of public spheres.