Although studying the actual use of L2 materials has gained momentum over the past few years, little is known about its synergy with teachers' beliefs. This study addressed this gap by exploring teachers' stated and enacted beliefs about (effective) materials use in L2 classroom discourse. To this effect, naturally-occurring interactions within 10 Iranian EFL classes were videotaped for three consecutive sessions. Then, the teachers were interviewed where they reflected on their transformations of textbooks. The data were analysed through document analysis of the textbooks, discourse analysis of the classroom interactions, and content analysis of the interviews. The findings showed that sheer convergence between what teachers think about materials (use) and what they actually do in the classrooms cannot guarantee the attainment of the intended and emergent goals of the lessons and/or activities. In-depth analyses indicated that there exist complex interrelationships between teachers' stated and enacted beliefs. Teachers' levels of understanding of their talk were found to mediate this interplay in classroom discourse. The findings can inform teaching process and teacher education programs by raising teachers' awareness about their actual use of materials and students' engagement in L2 classroom discourse.