This study is an investigation of the use of L1 in two sixth grade CLIL Geography and Home Economics classrooms in two Cypriot Primary schools. An overview of the international literature indicated that L1 is used in such classrooms for disciplining and instruction giving (Gierlinger 2007), group work (Dalton-Puffer 2007), text mediation and explanation of ideas (Buchholz 2007, Arthur and Martin 2006), off-topic talk(Nikula 2005) and label quests (Heath 1986, Arthur and Martin 2006). This study is ethnographically-informed as it employs fundamental elements of ethnography together with analysis of video-recordings of classroom interaction, a key characteristic of the micro-ethnographic approach (Erickson, 1996, 2004; Garcez,2008). The findings from 640 video recorded lessons (320 minutes of each subject) show that the functions of bilingual events span the single word to interactive exchange in length, and are evenly distributed across instructional and regulative registers (Christie 2000, Gardner 2006). The four-fold new classification identifies an expanded repertoire of word level bilingual events, including the L2>L1 label quests which are particularly important in CLIL contexts; a range of bilingual events including codeswitching for instructional purposes; a new category of events related to code management; and clear examples of regulative events such as disciplining and giving instructions that are well documented in the literature.