A reciprocal relation has been identified between teacher emotion and teacher professional identity. However, the underlying mechanism explaining this complex interaction remains underexamined. Moreover, limited attention has been paid to the emotional dimension of student-teachers' development of professional identity during university coursework. To bridge this gap, the present study explores how student-teachers' emotions reciprocally interact with their professional identities, drawing data from questionnaires, reflections, and interviews with students taking courses related to language teaching in a teacher-training university. Both quantitative and (...) qualitative data delineated the intertwined trajectories of student-teachers' emotional experiences and the development of professional identity in the learning process of becoming teachers. Mainly triggered by course-related factors, student-teachers experienced a wide array of emotions, of which the polarity and intensity were determined and mediated by their goals and actions deriving from their professional identities. Those aroused emotions, in turn, signaled the developmental process of professional identity and promoted or hindered their emerging identities. This paper concludes with some implications for initial teacher education programs. (shrink)