This chapter is about culture and mathematics teaching and learning. The authors' goal is to offer a thoughtful treatment of the role of culture in the teaching and learning of mathematics and to synthesize literature that is relevant to this concern from multiple subdisciplines in education, including math education, educational anthropology, sociology, sociolinguistics, and critical theory. Here, the authors consider boundaries between what is commonly thought of as "cultural" knowledge (that is, knowledge derived from settings outside of school, typically in students' homes and communities) and "domain" knowledge (that is, knowledge valued in the practices prescribed by mathematicians and math educators). They briefly explore relations between "everyday" informal math knowledge and school math as a way to begin the conversation about the cultural nature of mathematics. They attend to the ways in which the field has conceptualized how issues of culture matter in mathematics classes, highlighting three lenses that researchers have used to understand culture and math learning: (a) the way that language mediates knowledge; (b) features of math classrooms as contexts that support or constrain different forms of knowledge; and (c) the way that racialized identities and expectations play out in mathematics classes. They examine how these issues of culture have taken shape in conversations and research about reforms in mathematics education. They also explore distinct programs and approaches that offer tools and ideas for blurring the line between domain and cultural knowledge in mathematics, and briefly reflect on the implications of these issues of culture and math learning for teacher professional development. (Contains 1 table, 1 figure and 3 notes.)