Construction of concepts at micro and meso level in bilingual classroom interactions. In adopting an approach called multilingualism and cognition in discourse practices (Gajo 2014: 139), which brings together discourse analysis (Roulet et al. 1985; Roulet, Filliettaz & Grobet 2001), conversational analysis (Gülich & Mondada 2001) and research on multilingualism (Coste 1994; Gajo et al. 2008), this paper aims to describe specific features of the knowledge construction process in bilingual classroom interaction, on the basis of an analysis of the data collected in three bilingual classrooms and two subject disciplines (biology and history). The analysis will be undertaken at the micro and meso interactional level: the former focuses on the local, in situ organization of interaction and the later helps highlighting sequential organization of interaction and the relationship between planned and emergent didactic tasks and discourse activities. Since the relationship between planned and emergent aspects of knowledge in bilingual classroom is strongly affected by linguistic resources and their opacity (knowledge is constructed in a foreign language), the paper will concentrate on analyzing the relevance degree of language thematization, linguistic negotiation and metalinguistic activities in knowledge construction process.