Book excerpt: This book explores the role of identity in adolescent foreign language learning to provide evidence that an identity-focused approach can make a difference to achievement in education. It uses both in-depth exploratory interviews with language learners and a cross-sectional survey to provide a unique glimpse into the identity dynamics that learners need to manage in their interaction with contradictory relational contexts (e.g. teacher vs. classmates; parents vs. friends), and that appear to impair their perceived competence and declared achievement in language learning. Furthermore, this work presents a new model of identity which incorporates several educational psychology theories (e.g. self-discrepancy, self-presentation, impression management), developmental theories of adolescence and principles of foreign language teaching and learning. This book gives rise to potentially policy-changing insights and will be of importance to those interested in the relationship between self, identity and language teaching and learning.