Mathematics education researchers (MERs) engage in interdisciplinary collaborations that contribute to the mathematics education discipline. MERs' learned forms of work and discourse, i.e., practices, are particular to their mathematics education discipline and might not align with practices needed to conduct interdisciplinary work. We interviewed four MERs who were leaders of interdisciplinary groups to learn about practices they reported using while collaborating with their groups. Using qualitative content analysis, we describe five practices commonly reported by the four MERs. We argue that these five practices are central ways of knowing and doing for MERs when working in interdisciplinary groups. Our study contributes to the mathematics education discipline by unpacking practices MERs use to engage in interdisciplinary groups that are influenced by interpersonal relationships. [For the complete proceedings, see ED630210.]