The pedagogical and sociocultural functions of teachers' code-switching are an important factor in achieving the dual goals of content learning and language learning in bilingual programmes. This paper reports on an ethnographic case study investigating how and why teachers switched between languages in tertiary bilingual classrooms in Indonesia, where the main language of instruction was English. Data on code-switching were gathered in three classrooms over one semester, employing classroom observation with video and audio recording, semi-structured teacher interviews with some stimulated recall, and a focus group discussion. Transcripts of classroom interaction were examined using both an Interactional Sociolinguistics (IS) perspective and functional categories of code-switching. Teacher reflections were studied, and analysis indicated that teachers' code-switching was frequently used to support students to gain understanding of unfamiliar concepts, where the pedagogical focus was on the subject matter more than on language. It also involved managing students' behaviour and engaging in interpersonal and affective interactions with students. The teachers' code-switching thus frequently functioned as translanguaging in that it occurred as an intentional strategy for teaching in these bilingual classrooms, integrating the two languages in order to achieve better communication and engagement in learning.