Questions regarding whether a first or a second/foreign language should be used as a medium of instruction (MOI) in schools, and if yes, for whom, and when, have been enthusiastically debated in recent years in Hong Kong and many Southeast Asian societies. The public debates, however, have largely not been able to benefit from the existing international body of research in bilingual education as well as the educational experiences of other countries. The reason is that such knowledge is often either couched in specialized, technical language or scattered over diverse journals and books, which are often off-putting to teachers, parents, school principals, policy makers and the general public. There is an urgent need to critically integrate and review the international research literature with a view to informing public debates and policy making regarding the medium of instruction in Hong Kong and other Southeast Asian contexts. This book aims at meeting this urgent need by discussing, in accessible language, research findings on key concepts of bilingual education, and recent developments of bilingual education policies in Hong Kong, Singapore and Malaysia. Teachers, students and researchers in the areas of bilingual education, language policy and planning (LPP), and studies of medium of instruction policy and practice both in Hong Kong and other Southeast Asian contexts will benefit from the book. Government officials and policy makers involved in language policy and planning, as well as school principals, parents and university administrators will also find this book especially useful in providing them with a research-based LPP framework for thinking, discussing and studying about important issues in LPP in their respective contexts.