This paper presents aspects of a study that aims to describe and make sense of changes over time in the intellectual field of mathematics education research. Drawing on the work of B. Bernstein, especially his essay on intellectual fields and knowledge structures, the paper seeks to raise questions about the fields standing in the wider field of intellectual knowledge production, the position of the fields actors in their own field, and their positioning vis-a-vis the official and public discourses and everyday school practice. Underpinning these questions is the view that changes in power relations are inscribed in the form of research activity that shapes the field, and that such changes are expressed in the mode of regulation that affects the identities of actors in the field. To study changes in the form of specialization of research activity and to give a systematic yet critical account of the field, researchers produced an empirical description and at the same time attempted to generate a language capable of showing the effects of that which it describes. The method of working was to look at a representative sample of published papers in the field to develop a tool for recording and analyzing these texts, and to create a model to help interpret the data. As well as presenting and demonstrating the usefulness of the analytical tool in the resulting description of the data, the paper sketches a provisional picture about the state of the field that captures the changing nature of its discourse, and depicts the positions it creates for the actors in the field, through the resources it makes available to them. This provides evidence to argue that researchers identities in mathematics education research bear the mark of a historical turn in educational studies, the knowledge structure of teacher education, toward its technologizing," and also the marks of the current mode of its regulation, which tends to produce identities with products that have an exchange value either in their own field or the field of supposed application. Three appendixes contain supplemental information in table form. (Contains 11 tables and 32 references.) (SLD)