The pace of change in today's society means that there is an ongoing need for teachers to learn, have new knowledge and use new pedagogical approaches to meet the needs of their pupils. For many teachers, this requires redefining their identity as teachers and what "teaching" means in 21st century learning environments. These changes also require teachers to be supported in learning to "teach" in different ways that are relevant to their own individual needs and to the contexts in which they work throughout their career. In this article, it is argued that a more integrated and collaborative approach to teacher education is needed with better understanding of those who take up the roles of teacher educator across a teacher's career. With a particular emphasis on "teacher educators" working in school to support teachers' career-long professional learning it is argued that currently many do not recognise themselves as teacher educators nor are they recognised by those they work with as teacher educators. Drawing on an empirical study carried out with mentors in schools in Scotland, it is suggested that these teacher educators may be "unrecognised" and remain "hidden professionals" because of the identities they construct for themselves, the values and priorities that they or others attach to their roles or because of the institutional structures and cultures in which they work. It is concluded that it will be difficult to recognise and value these "hidden teacher educators" and the distinctive contribution they can make to teachers' career-long professional learning without further clarification by them and others of the roles and responsibilities they hold.