Couple satisfaction has been extensively investigated, but little attention has been paid to the nature and assessment of high‐quality, flourishing couple relationships. Particularly, current measures of relationship quality are insensitive at the upper end of the continuum, which in turn hinders progress toward understanding and facilitating flourishing couple relationships. Drawing on concepts developed in positive psychology, we proposed a theoretical framework of couple flourishing that incorporates hedonic and eudemonic components. Items to assess these aspects of couple flourishing were generated and administered online to a sample of 1,116 participants. Using combined methods of classical test theory and item response theory (IRT), we selected the most informative items to form 4‐, 8‐, 16‐item versions of a Couple Flourishing Measure (CFM). IRT analyses show that the CFM discriminated variation at the upper range of relationship quality better than widely used measures of relationship satisfaction. Confirmatory factor analysis showed that couple flourishing was related to, but distinguishable from, relationship satisfaction. In an independent sample of 330 participants, we replicated the unifactorial structure of the CFM, and the distinguishability of couple flourishing from couple satisfaction. This research offers new insight into the concept of relationship flourishing. The sensitivity of the CFM at the high end of relationship quality makes it possible to test for predictors of relationship flourishing and evaluate interventions that seek to enhance flourishing.