In 1994, a group of professionals involved in mathematics education convened at Gallaudet University to discuss the state of mathematics education for deaf and hard-of-hearing (DHH) students. The result was the National Action Plan for Mathematics Education Reform for the Deaf (NAPMERD) (Dietz, 1995), which proposed recommendations for changes in curriculum, pedagogy, teacher preparation, assessment, and research. Since that time, however, student performance in mathematics computation and problem solving, as measured by standardized assessments, has not significantly improved (Allen, 1995; Broadbent & Daniele, 1982; Traxler, 2000). Deaf and hard-of-hearing students continue to perform well below grade level in mathematics, graduating on average with less than a sixth grade achievement level. In light of the NAPMERD report, this chapter provides an overview of research regarding the mathematics instruction and learning of DHH students over the past 25 years (encompassing the 11 years leading up to the NAPMERD report—and coinciding with the beginnings of the National Council of Teachers of Mathematics education reform movement—and the 14 years since). Specifically, this review summarizes what is known regarding the deaf learner’s understanding of mathematics and performance with related concepts and the mathematics instruction received by the deaf learner, as well as possible factors surrounding these topics. The chapter highlights gaps in the knowledge base pertaining to mathematics instruction and learning with this population and suggests areas for future research.