Borders--territorial, economic, political, and ideological--are processes of social division. They monitor and exclude and are regulated, patrolled, and maintained by an array of power regimes, but borderlands are also sites of movement, agency, and resistance. Likewise, mathematics is used as a border that divides and politicizes. In this article, we seek to explore how the field can disrupt and transform borders in mathematics education. We draw on border and third space theories to challenge the ontological and epistemological borders in mathematics education that are taken as normative yet reify exclusion through the following questions: (1) What is mathematics? (2) Who can do mathematics? (3) Where is mathematics done? We situate these questions within the COVID-19 pandemic as context of continued injustice. We call for the field to be disobedient and ready itself for the changes that must come so the field can create a humanizing and just alternative.