It has been recognized for some time that the use of language is not only relevant to language instruction, particularly German language teaching, but also plays a significant role in subjects such as mathematics or the natural sciences for the success of teaching. In light of the increasing heterogeneity among students, raising awareness and generating knowledge about the importance of language in subject teaching is essential. This volume exemplifies how linguistic competencies are significant in subject instruction, specifically in mathematics education. It brings together contributions that address the question of language in the subject of mathematics across different grade levels. By consolidating these contributions, it provides both current assessments of the subject of mathematics at various school levels and future perspectives.