This document discusses code mixing and code switching in language use. It begins by defining bilingualism as the ability to use two languages. Code mixing occurs when elements of one language are transferred into another language in communication. Code switching refers to changing between two languages above the clause level. The document then provides examples of code mixing and code switching between English and Indonesian. It discusses how teachers often use code mixing to help students understand lessons. The research questions examine the types and most dominant forms of code mixing used by an English teacher in their classroom.