The contributions in this volume combine to show how views of language and of language research in mathematics education have changed significantly in recent decades, and how they will continue to change and become even more complex and challenging in the era of diversity. All of these contributions by leading scholars are grouped into two sections for emphasis on issues of: • Theorising the complexity of language in mathematics teaching and learning • Opening spaces of learning with mathematics classroom research on language This book will be of great interest to mathematics teachers, teacher educators, curriculum developers and mathematics education researchers who deal with the study and implementation of pedagogies of mathematics teaching and learning, specifically in regions of the world which are culturally and sociolinguistically diverse.