This study investigates how relevant indicators of teachers' sense of their professional identity (job satisfaction, occupational commitment, self-efficacy and change in level of motivation) are related. A model is proposed, tested with structural equation modelling (SEM) and refined using data from 1,214 Dutch teachers working in secondary education. Classroom self-efficacy and relationship satisfaction play a key influencing role in the relationships between the indicators. Using multiple-group SEM, the parameters of the overall model are similar for the novice, experienced and senior teachers in a constrained model. This aspect of similarity across experience groups is in line with findings of previous research on teachers' professional identity. The present study contributes to the further development of a solid theory on teachers' professional identity, which has been lacking. (Contains 5 tables, 2 figures and 1 footnote.)