This textbook uses analysis of interaction in a range of teacher education and professional practice settings in ELT to explore the different identities and power relationships which teachers orient to. It traces the role of identity and interaction in the processes of acquiring new teaching skills and knowledge, reflecting on professional practice and constructing teaching selves, and explores the limits and constraints on these processes imposed by global forces such as the marketization of education. The book is written for teachers, teacher educators, postgraduate students and researchers interested in the relationships between social interaction, identity and professional practice in ELT. It is suitable for use in conjunction with any postgraduate-level course on language in interaction, as it surveys and critically discusses various approaches and includes many practical examples.