This book is a review of more than twenty years of international research on teacher educators. It offers a solid overview of what is known about the professional roles, professional behaviour and professional development of teacher educators. A systematic analysis of the focus, methods and data sources of 137 key publications on teacher educators make this book into an important reference work for everyone interested in the work of and research on teacher educators. There is a growing consensus that teacher educators largely determine the quality of teachers and hence, the quality of education. Through this book, Lunenberg, Dengerink and Korthagen provide not only insights into the various roles of teacher educators and the complexity of their work, but they also discuss building blocks for ongoing structured and in-depth professional development. The authors clarify that if we wish to take 'being a teacher educator' seriously, it is imperative that we build our understanding on research data. The book shows that although the number of studies on teacher educators is growing, the research in this field is still scattered. The authors highlight the need to create a coherent research programme on teacher educators and provide concrete suggestions for such a programme.