The development and iteration of a body of professional knowledge appropriate to the demands of practice is a central concern of studies of professional education and work. This article concentrates on Bernstein's notion of the 'region' of professional knowledge, identifying regions as complex socio-epistemic entities into which forms of knowledge are appropriated and transformed to meet the requirements of practice. In order to better understand the constitution of professional knowledge, there is a need to conceptualise how knowledge is recontextualised between regions, disciplinary 'singulars', and professional practice. Two variables, proximity and dominance, are introduced to illustrate how relations between regions, singulars and practice may vary, with implications for what is recontextualised into regions. In some professions, there are pressures for greater proximity between regions as a consequence of changes in work practices, while in others there is the potential for the dominance of recontextualisation processes by market and bureaucratic logics. It is suggested that actors within regions need to find ways to maintain authority over professional knowledge while avoiding the risks of control by bodies ill-equipped to maintain knowledge validity. The analysis provides a lens through which to view developments in the knowledge bases of professional, or professionalising, occupations, and concomitant changes in professional education.