Three studies were undertaken to develop the Positive-Negative Relationship Quality scale (PN-RQ), conceptualizing relationship quality as a bidimensional construct in which the positive qualities of a relationship are treated as distinct from its negative qualities. Analyses in emerging adults (Study 1: N = 1,814), in online respondents (Study 2: N = 787) with a 2-week follow-up, and in a single group pre-intervention-post-intervention study (Study 3: N = 54) of the Promoting Awareness, Improving Relationships (PAIR) program provided support for (a) positive and negative qualities as distinct dimensions via confirmatory factor analysis (CFA), (b) the PN-RQ representing an item response theory-optimized measure of these 2 dimensions, (c) substantive differences between indifferent (low positive and negative qualities) and ambivalent (high positive and negative qualities) relationships potentially obscured by unidimensional scales, (d) high levels of responsiveness of the PN-RQ scales to change over time, (e) the unique predictive validity offered over time by the PN-RQ scores beyond that offered by scores of current unidimensional measures of relationship quality, and (f) the unique longitudinal information gained by using the PN-RQ as a bidimensional outcome measure in an intervention study. Taken together, the studies offer promising support for the PN-RQ scales suggesting that they have the potential to advance both basic and applied research. (PsycINFO Database Record