In order to position the notion of identity as more central to theory and practice in TESOL, a survey is presented of how the notion of identity contributes to our understanding of the nature of the teacher self, second language learning and teacher learning in language teaching. Available theory and research is reviewed to illustrate the sources of teacher and learner identity and the multifaceted ways in which aspects of identity shape their approaches to learning and the impact identity can have on beliefs, attitudes, motivation and classroom practices as well as their use of English. Suggestions are given as to how a focus on identity can be included in teacher education courses for language teachers.