Many empirical studies have shown that students’ mathematical difficulties are often connected to language factors. In this chapter, we discuss this issue from different perspectives and with regard to different groups of students. First, differences between everyday and academic language on word, sentence, and text/discourse level and their implications for mathematics learning processes are discussed. Secondly, it is described how language factors affect the achievement of specific groups of students: second-language learners, students with learning disabilities in mathematics and reading, and students with specific language impairment. Thirdly, important language dimensions for the mathematics learning focusing on the use of language as a learning medium and discourse practices are presented. Finally, it is concluded that instructional approaches seem to become most effective for supporting mathematics learning when they provide learning opportunities especially for the discourse practices of explaining meanings of mathematical concepts and operations and for describing general pattern.