A synthesis of reasons for the production of this monograph is presented with a focus on contemporary research in the context of the Ninth Congress of the European Society for Research in Mathematics Education. Within the domain of mathematics and language, three lines of concern are addressed: (1) classroom discourse, (2) language diversity, and (3) conceptualization through language. Each line of concern is respectively illustrated by pioneering results from Ruthven and Hofmann, Barwell, and Edmonds-Wathen. An argument is made about the wide scope, depth and richness of this domain as well as the challenges involved in its development.