This paper explores an aspect of the knowledge of teaching required by teacher educators and how that knowledge might be developed if teaching (about teaching) is to be conceptualised as a distinct and important field in its own right--with its own forms of knowledge, ways of working and perspectives on the world. The paper focuses on self-understanding as a component of teacher educators' knowledge of practice and examines how the development of self-understanding can be conceived as a form of teacher educator expertise. Few studies have explicitly considered teacher educators' self-understanding as a form of professional knowledge; hence, this article makes a contribution to explicating and documenting this aspect of teacher educators' practice.