This paper addresses the language usage at one Swedish upper secondary school offering content and language integrated learning (CLIL), with a focus on how language choices are made by both teachers and students during the lessons. The translanguaging strategies used in the classroom were studied over the course of one academic year (2011-2012). Data collection included audio recordings, participant observations, field notes and artefacts as well as semi-structured interviews with both individuals and focus groups. The results included in this presentation focus on one maths and physics teacher who has developed and currently implements translanguaging strategies in his teaching of students (ages 15-16) in their first year of a program of study in natural sciences. During his lessons, language usage was noted, indicating the language being used (i.e. Swedish or English), the activity being conducted, the modality (reading, writing, listening, speaking), and the actors in the specific activity. Preliminary results indicate that the students generally take their language cues from the teacher and do not usually switch languages unless he does, that Swedish is used nearly exclusively for all social interaction in the classroom, and that both students and the teacher find it useful to have maths and physics textbooks in both English and Swedish. The interview with the teacher provided insight into how he has developed his strategies using multiple language resources over his nearly 15 years of CLIL experience. The presentation will include examples from classroom interaction as well as teacher and student perspectives from the interviews. The results are part of a current doctoral research project addressing CLIL in the Swedish context and thus this paper will be presented in relation to the larger investigation.