Mutually responsive orientation (MRO) reflects a system of reciprocity between members of a dyad (Kochanska, 2002), and MRO observed in parent-child relationships is a robust predictor of child development (Kim, Boldt, & Kochanska, 2015; Kim & Kochanska, 2012; Kochanska, Aksan, & Joy, 2007; Kochanska, Forman, Aksan, & Dunbar, 2005). The goal of the present study was to adapt an observational coding system previously validated in parent-child dyads to assess MRO in intimate relationships and test the reliability and validity of scores from this adapted coding system. One hundred and fifty-nine couples were observed engaging in a series of standardized, naturalistic, interactive contexts. A team of trained behavioral coders rated MRO across several paradigms. Participants also completed semistructured interviews and self-report questionnaires assessing numerous dimensions of intimate relationship quality to assess convergent and divergent validity and individual and relationship health outcomes to assess criterion and incremental validity. Interrater reliability estimates established that multiple coders could reliably rate MRO across multiple contexts. As anticipated, MRO had small to moderate correlations with other relationship processes (e.g., conflict management, support), demonstrating that MRO is a unique but related dimension of intimate relationship quality. MRO scores were also associated with numerous outcomes including global relationship satisfaction, relationship security, partner mental health, and parent-infant bonding, even when controlling for neuroticism. The assessment of MRO in intimate relationships holds promise for tapping into a unique dimension of intimate relationship quality with implications for explaining a range of outcomes of interest to couples researchers. (PsycInfo Database Record (c) 2020 APA, all rights reserved).