With emphasis on teacher and learner code-switching patterns, this book is one of the first studies to comprehensively address these issues in English as a Foreign Language (EFL) classrooms. The author examines teacher and learner code-switching through quantitative analysis, discourse analysis, conversation analysis, and mixed methods used in the study of code-switching. She addresses current debates on the amount of first language (L1) use, the functions of L1 use, the functions of teacher only code-switching patterns and the functions of teacher and learners shared code-switching patterns in foreign language classrooms. The book explores the implications of EFL classroom code-switching and how this can feed into better understanding of foreign language learning and teaching, language teacher development and new research directions in TESOL and applied linguistics. The principles and discussions of EFL classrooms are easily generalised to other language classrooms. This book will be of interest to researchers in the fields of second language acquisition, applied linguistics, and ELT, as well as researchers in the fields of sociology, education, and ethnomethodology.