This thesis studies specialist differentiation in the surgical profession of the United Kingdom, seeking to clarify what the combinations of factors favour or hinder it. It draws on interviews with two hundred surgeons, general practitioners and hospital CEO’s, as well as on sociological literature, especially Bucher and Strauss’s (1961) ‘Process Model’, the concept of ‘profession’ developed by Freidson (1970), Larson’s (1977) model of the ‘Professional Project’ and Bourdieu’s (1981, 1984, 1986, 1988, 1990, 1991, 2005) seminal work on ‘Capital’ and ‘Power’ in ‘Social fields’. The thesis aims to interpret specialisation as a dynamic political process influenced by different groups’ deployment of accumulated specific types of ‘capital’, challenging the view, widespread in the profession itself and still present in functionalist sociological literature, that specialist differentiation is an inevitable consequence of advances in knowledge and technology. In addition to the introduction, conclusion and appendices, the thesis includes chapters on: (1) theoretical framework; (2) methodology; (3) the role of knowledge and technology in specialist differentiation; (4) the role of institutions before the establishment of the NHS; (5) the role of the relationship between the profession and the state in the period 1948-1990; (6) ditto in the period 1991-1997; (7) the current situation and how it might develop.