This article considers teacher professionalism from a neglected perspective. It analyses assumptions about the dynamics of professional participation implicit within competing academic and policy constructs of professionalism, including the currently iconic concept of "communities of practice". All entail notions of becoming and being a professional. However, data from the project "Transforming Learning Cultures in Further Education" (TLC) reveal significant instances of "unbecoming": a majority of the tutors participating in the project were heading out of further education (FE) teaching. This illuminates a broader problem of exodus from the sector, in a political context which privileges economic goals and targets at every level, and in which the current climate of performativity increasingly impacts upon pedagogical relationships--contextual conditions which are also highly relevant to schooling and higher education. Drawing on exemplar case studies of two tutors, and on the theorization of learning cultures emerging from the TLC project, a Bourdieusian analysis of these dynamics is developed in terms of the interaction of habitus and fields, and "communities of practice" critiqued. Paying particular attention to policy-driven changes in and to the field of FE, and to the cross-field effects in FE of policies in other sectors of education and beyond, the article argues for a more dynamic notion of professional participation. This might underpin "principles of procedure" for improving teaching and learning, and policies to support diverse forms of teacher professionalism throughout the education system. (Contains 3 notes.)