In the complex, multilingual societies of the 21st century, codeswitching is an everyday occurrence, and yet the use of students' first language in the English language classroom has been consistently discouraged by teachers and educational policy-makers. This volume begins by examining current theoretical work on codeswitching and then proceeds to examine the convergence and divergence between university language teachers' beliefs about codeswitching and their classroom practice. Each chapter investigates the extent of, and motivations for, codeswitching in one or two particular contexts, and the interactive and pedagogical functions for which alternative languages are used. Many teachers, and policy-makers, in schools as well as universities, may rethink existing 'English-only' policies in the light of the findings reported in this book.