Teacher professional identity is conceptualized in this chapter as a complex configuration of personal and contextual factors. Professional identity is also seen as dynamic and subject to change. This coloring of the concept leads here to a specific elaboration of research with regard to (student) teachers’ identity formation. This research then focuses on (student) teachers working on issues arising from tensions between the personal and the contextual, the ways in which they position themselves toward relevant others, the impact of the micropolitical reality of the school on their functioning and well-being, and the role so-called “stories to live by” play in their work. The operationalization of the concept is illustrated by two studies in which the complexity and uniqueness of (the development of) professional identity have been investigated using narrative methods and techniques. This chapter also distinguishes between two different but related internal processes that are important in teacher education, namely professional learning internalizing knowledge and skills that are generally found to be relevant for the profession, i.e., teaching competence) and identity formation (a personal process of validating learning experiences in light of one’s “image-ofself-as-teacher,” that is, the teacher that one is and wants to become). It is argued that both processes can reinforce and enrich each other and, as such, will result in a more comprehensive and coherent framework for understanding teachers’ professional work and their development as teachers. An attempt is made to present both internal processes in an overarching model, referred to here as “framework of professional identity learning.” The chapter concludes with suggestions for (follow-up) research.