Connecting diverse theories and practices in English-medium Instruction (EMI) implementation, this book provides a comprehensive and systematic overview of EMI in K-12 settings in the Asian and European contexts. It addresses a wide range of ongoing challenges faced by many EMI policymakers and teachers and offers potential solutions or coping strategies. While it focuses on the contexts of Asia and Europe, the book can also provide inspirations or suggestions for researching and implementing EMI in other geographical or cultural contexts such as Africa. In brief, this book aims to (1) discuss up-to-date theories on EMI from different fields of research including language policy studies, applied linguistics and CLIL research, (2) provide detailed and critical reviews of EMI policies in K-12 education in the broad Asian and European contexts, (3) report empirical, classroom-based research on EMI implementation in these contexts and compare findings with those of the previous research, (4) engage different researchers and scholars from relevant fields in a dialogue about EMI-related theories, issues and challenges in these contexts and (5) serve as a hands-on resource for educational practitioners who are (interested in) practicing EMI.