This qualitative study explores Teaching Assistants’ (TA) beliefs and practices related to the role of textbook materials in foreign language (FL) teaching and learning in beginner-level courses. Results, interpreted from a sociocultural theory perspective, indicate that the textbook was an important tool mediating instructional planning and student learning of FL vocabulary and grammar, but it was considered less valuable for student-to-student oral activities and for teaching culture. The powerful influence of participants’ cultural backgrounds was demonstrated as differences emerged in how native speakers and non-native speakers of the FL taught used textbook materials although they had pedagogical coursework and FL teaching experiences in common. Implications include a call for Language Program Directors (LPD) and teachers, including novice TAs, to collaborate on strategies for best practices in textbook use.