Driven by the concept of mediation, this study is set out to use sociocultrual theory as the theoretical framework to explore the mediation role of textbooks, specifically, the series Northstar in English as a Foreign Language (EFL) university classes in Vietnam. Learning journals with guided questions are employed to collect data on how different aspects of English textbooks assist students’ learning in the classroom. Besides, transcripts of recorded classroom obervations are analysed to interpret how the textbooks formulate and faciliate students’ ideas related to the given tasks and generate their interaction in both the target language and the mother tongue. It is found from the students’ journals that the textbooks assist them in understanding the lesson contents and the images help them with visualizing the lessons. Besides, the students make use of the tasks/activities when practising language skills, especially the listening skill. The transcripts reveal the process in which students refer to their previous knowledge related to the topics/tasks provided in the textbooks to interact with one other. More speficially, the tasks and the ideas of other group members mediate more thoughts of the students, leading to collective knowledge construction and task completion. From the findings, recommendations for the use of textbooks in the framework of sociocultrual theory are put forward.
