This research looks into how Indonesian and English are used together in classroom interactions, particularly in English lessons at SMAN 5 Enrekang. Code switching, where people switch between two or more languages or language variations in a conversation, is the main focus. The study aims to find out why and how teachers and students use code switching in the classroom. This research uses a descriptive qualitative approach, involving observations and interviews. It identifies several functions of code switching, such as clarifying messages, specifying who is being addressed, repeating, adding new elements, and personalizing or objectifying. The findings suggest that code switching helps students understand English better at different proficiency levels and keeps classroom interactions effective. Interviews with teachers and students reveal that factors like the teachers' skills and experience, students' language levels, changes in classroom situations, and the switch from formal to informal language all influence code switching. The global status of English also affects how code switching occurs. The study uses frameworks by Marasigan (1983) and Fishman (1976) to explain the functions and factors behind code switching in educational settings. This research aims to improve teaching strategies, teacher training, and future studies. It shows that code switching can make complex ideas clearer, enhance understanding, and create a more inclusive learning environment. Thus, it is a useful strategy for boosting student engagement and comprehension during lessons.