This article uses a conversation analysis methodology to examine how lexical Focus on Form is interactionally accomplished in teachers' vocabulary explanations in secondary Content and Language Integrated Learning (CLIL) classrooms. Recent conversation-analytic work has focused on the interactional organisation of vocabulary explanations in second/foreign language classrooms, but there is a lack of research that explores this phenomenon in CLIL contexts. Based on a corpus of 12 secondary CLIL lessons, this article provides an account of (a) the interactional organisation of vocabulary explanations in CLIL lessons, (b) the resources used in their construction and (c) how they reflect participants' orientation to an institutional goal in CLIL of teaching language.