This study examines interactions in non-English major large classes in Vietnam. Audio recordings of classes of economics and business were used for data analysis. The study adopted sociocultural discourse analysis (Mercer, 2004) which focuses on the use of language as a social mode of thinking and a tool for teaching-and-learning, constructing knowledge, creating joint understanding and tackling problems collaboratively. The findings show that teachers mediated learners with their prompts, questions and scaffolding. Interactions between teachers and students assisted students in understanding and building concepts related to their majors, learning English language expressions and vocabulary.