Scholars have called for new conceptualisations of teachers' learning that capture the complex, contextualised, and dynamic nature of professional growth. In this article, we describe the Dynamic Systems Model of Role Identity (DSMRI) that portrays teacher learning as inseparable from the complex and dynamic processes by which teachers form their professional identities. The model depicts theoretical and procedural learning about teaching as integrated with other ontological and epistemological beliefs, self-perceptions and self-definitions, purpose and goals in teaching, and perceived action possibilities that constitute the teacher's professional role identity. After describing the DSMRI, we demonstrate its application with an instrumental case of a science teacher who participated in a professional development (PD) institute designed to foster learning and motivation for implementing student-centred, inquiry-based instruction. DSMRI-guided analysis of pre-, mid-, and post-institute interviews highlighted the role of pre-PD role identities of learner and teacher in the teacher's PD experiences, which, in turn, fostered both new alignments and new tensions in the teacher's role identity that promoted an overall change towards a more student-centred teacher role identity. The article demonstrates the utility of the DSMRI for conceptualising teachers' learning as contextualised and dynamic identity formation processes.