Vocabulary understanding is a major contributor to overall comprehension in many content areas, including mathematics. Effective methods for teaching vocabulary in all content areas are diverse and long standing. Teaching and learning the language of mathematics is vital for the development of mathematical proficiency. Students' mathematical vocabulary learning is a very important part of their language development and ultimately mathematical proficiency. This article draws on current research-based evidence to (a) provide a rationale for teaching vocabulary, (b) offer a review of research that supports the importance of teaching mathematics vocabulary, and (c) describe specific strategies for teaching mathematics vocabulary. It also addresses implications and the need for future research.