Objective: This study reports on the operationalization and testing of the newly developed Relationship Quality (RQ) scale, designed to assess an individual’s perception of his or her RQ in their current partnership. Methods: Data were generated through extended sampling from an original U.K.-based research project, Enduring Love? Couple relationships in the 21st century. This mixed methods study was designed to investigate how couples experience, understand, and sustain their long-term relationships. This article utilizes the cross-sectional, community sample (N = 8,132) from this combined data set, drawn primarily from the United Kingdom, United States, and Australia. A two-part approach to scale development was employed. An initial 15-item pool was subjected to exploratory factor analysis leading into confirmatory factor analysis using structural equation modeling. Results: The final 9-item scale evidenced convergent construct validity and known-groups validity along with strong reliability. Conclusion: Implications for future research and professional practice are discussed.