The purpose of this qualitative multiple case study is 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. 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 relationship between these two perspectives and the participants' discipline; and (c) a similar occurrence, both in terms of nature and frequency, of the MMR quality criteria most mentioned by the participants across disciplines. Implications of the findings for the field of MMR are discussed.