This chapter introduces bilingual education and, in particular, translanguaging, one of the key concepts and focus of this book. First, we discuss their definitions, tracing the emergence of bilingual education from monolingual education via various means, notably, CLIL, and its establishment in various locations, particularly the US, and its spread to the rest of the world. Following this, we introduce key theoretical concepts, associated with translanguaging, including Cummins’ ‘common underlying proficiency’. We also explore the wider implications of bilingual education, touching on its effects on cognitive development, contributions to social justice, and its influence on teacher identity. Finally, we address the challenges and pedagogical considerations that arise, particularly in an English as a foreign language (EFL) context. This chapter also lays the ground for a more detailed examination of both translanguaging and EFL contexts in the next chapters.