Abstract Driven by Beijaard, Verloop and Vermunt’s (2000) theory of Professional Identity (PI), this study aims to investigate teachers’ perception of their PI in relation to the English textbooks they use in EFL classes. In-depth interview with four Iranian EFL teachers and the school principal was conducted. The teachers’ reports were employed to investigate their PI in relation to the textbooks they used. Furthermore, the school curriculum was analyzed through an interview with the school principal and examining the school documents. Content analysis of the interview data revealed that all the teachers viewed the content knowledge dimension of their PI reliant on the textbooks. Over the years, they had gained more autonomy in adapting the content or selecting more supplementary sources. Overall, the participants in this research highlighted the pivotal role of textbooks in the construction of their PI, most importantly in the formation of their content knowledge and the least in the development of their pedagogical knowledge. The analysis of the school curriculum revealed a heavy reliance of many decisions on textbooks directly or indirectly. The findings in this study will provide more insights for curriculum developers, language school managers, teacher educators and teachers who have a say in curriculum decisions when learning about the crucial role of textbooks in PI.
