How do aspiring English teachers develop professional identities during their studies? What role do their individual language learning biographies play in this process? The author examines the relationship between language learning biography and professional identity formation through a multi-perspective and iterative approach, which makes the fleeting and multifaceted nature of identity productive and tangible for research in foreign language teacher education. On a theoretical level, she explores the concept of identity in terms of its structure and genesis, linking it to concepts of transformative education and subjectivation. In the methodological section, a combined research approach of Grounded Theory and narrative analysis is developed for the empirical turn of the concept. Two case studies then illustrate how richly nuanced and contrasting teacher education students construct their identities as learners and teachers of the English language.