In this chapter, I focus on the ethics encapsulated in mathematical knowledge. I assume that there is more to our relationship with mathematics than just teaching and learning it. Ultimately, learning mathematics is not just about the knowledge we gain: crucially, it is also about what we do on the basis of that knowledge. This represents a significant ethical stance. Therefore, in this chapter, I do not focus on what counts as mathematical knowledge or on different ways of teaching and learning mathematics, but instead on the ethics of mathematical knowledge. In other words, how do we become ethically responsible with the knowledge we call mathematics?