Doctoral supervisors’ conceptions of quality indicators of mathematics education research and of a mathematics researcher were investigated as a part of a more comprehensive study investigating a doctoral program (DP) at a Nordic university. The data set consisted of transcribed interviews with five supervisors, which were analysed by an inductive coding process. Findings revealed that supervisors’ conceptions of quality indicators of mathematics education research were built on a major understanding, the Chain, which refers to the connectedness and coherence of research processes from the purpose until the conclusions. A mathematics education researcher should be able to perform this Chain and also have certain competencies such as knowing the field, being open-minded, and having communication skills, mathematics knowledge and classroom experience. The implications for DPs are discussed.