The book "Code-switching in Indonesian as a Second Language Classrooms" examines the role of code-switching (CCS) in teaching and its impact on understanding and the effectiveness of learning in Indonesian classrooms. Through a qualitative study that employs ethnographic methods such as recordings, interviews, questionnaires, and direct observations of classroom interactions, the author highlights the functions and reasons for code-switching by both teachers and learners. The findings show that both teachers and learners use CCS to manage various tasks in the classroom and that it serves as a strategy to support the learning process. These insights contrast with earlier studies that viewed CCS as an obstacle to language acquisition.