While teachers’ confidence in their abilities is a crucial asset in teachers’ professionalism and their identity development, their efficacy doubts are also considered useful. Given the diversity of English Language Teaching (ELT) contexts, this paper probes the dynamic nature of efficacy doubts the teachers face and are expected to resolve in English for General Purposes (EGP) and English for Specific Academic Purposes (ESAP) instruction. To this end, based on the existing theoretical frameworks in EGP and ESAP methodology and interviews with 25 university English teachers, two questionnaires were developed and administered to 170 Iranian EGP and ESAP university instructors. The results of factor analysis confirmed five factors underlying ESAP teachers’ teaching efficacy doubts and four factors for EGP teachers’ teaching efficacy doubts. The results may promise implications for ESAP and EGP teacher education programs teacher educators may address the common efficacy doubts identified in this study and expose the current in-service and future ESAP and EGP teachers to the typical factors which may potentially hamper their efficacy and help them resolve their efficacy doubts as a means towards professional development.