The purpose of this qualitative multiple case study was to describe and compare how researchers in the education, nursing, psychology, and sociology disciplines operationalize and conceptualize the quality of mixed methods research (MMR). An international sample of 44 MMR researchers representing these four disciplines were interviewed by Skype and telephone. The study findings point to: (a) two perspectives from which the quality of MMR is understood, one contingent and flexible and the other universal and fixed; (b) a link between these two perspectives and the participant’s own discipline; and (c) an equal prevalence of the criteria most mentioned by the participants across disciplines. Implications of the findings for the field of MMR are discussed.