This study investigates the interactional unfolding of student smiles in instructed language learning settings drawing on data from both English as a Second Language and as a Foreign Language classrooms. Conversational actions performed by participants through 'smiles' is an under-researched area, especially in classroom settings where teachers' and students' smiles may serve different functions due to the institutional nature of ongoing interactions. To address this research gap, we aim at investigating the interactional unfolding of student smiles in English language classrooms based on 16 h of video-recordings in Luxembourg and 45 h of video-recordings in the US. Taking a conversation-analytic approach, we show how participants use smiles to index and resolve interactional trouble. Our analysis shows that smiles and epistemic issues in the classroom are intricately connected, and in the case of interactional trouble related to epistemic access, student smiles serve to maintain affiliation and to promote the progressivity of talk. The findings of the paper have implications for understanding the interactional unfolding of smiles in institutional interaction in general, and in classroom interaction in particular. (C) 2015 Elsevier B.V. All rights reserved.