This book offers an international perspective on the current and future state of the research specifically focused on the role and use of language in mathematics school teaching and learning. It focuses on the development of a unified view of the languages of the learners, of the teachers and of mathematics by considering the role of language in the learning, teaching and doing of mathematics in the classroom, and the current richness and pluralness of language and culture. Twelve contributions show together how views of language and of language research in mathematics education have importantly changed in the last decades, and how they will continue to change and become even more complex and challenging in the era of diversity. All 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 world regions culturally and sociolinguistically diverse.