Drawing on previous research that focused upon the formation and mediation of teacher professional identity, this paper develops a model for conceptualising teacher professional identity. Increasingly, technical-rational understandings of teachers' work and "role" are privileged in policy and public discourse over more nuanced and holistic approaches that seek to understand teacher professional identity--what it is to "be" a teacher. This article seeks to offer an alternative view, presenting the idea that an understanding of the processes by which teacher professional identity is formed and mediated is central to understanding the professional learning and development needs of teachers and advancing a richer, more transformative vision for education. I argue that instrumentalist notions of teachers' work embedded in neo-liberal educational agendas such as those currently being advanced in many western countries offer an impoverished view of the teaching profession and education more broadly, and suggest that the concept of teacher professional identity holds the potential to work as a practical tool for the teaching profession and those who work to support them in the development of a more generative educational agenda. (Contains 1 figure.)