The ability to respond flexibly in situations is critical to individual well-being and couples’ functioning in romantic relationships. The Flexibility in Partner Perspectives Scale (FiPPS) was developed and validated so that two key aspects of relational flexibility—specifically the ability to generate alternative perspectives and respond non-defensively when alternative perspectives are raised within challenging partner situations—can be studied and targeted in interventions for distressed couples. We introduce the FiPPS as an 8-item self-report questionnaire composed of two 4-item subscales that measure these aspects, respectively. In Study 1, individuals (N = 208) in committed relationships were recruited online to answer questionnaires relating to relational flexibility and various aspects of the couple’s and individual’s functioning. We used parallel analysis and exploratory factor analysis to examine the psychometric properties of the 25 items developed for the FiPPS and to reduce the number of items retained in the final measure. The FiPPS was then validated in Study 2 using confirmatory factor analysis with a separate online sample of individuals (N = 430) in committed relationships. A subset of Study 2’s sample (N = 196) was used to establish test–retest reliability. Studies 3 and 4 demonstrated FiPPS’ predictive validity by showing in two additional samples (N = 260 treatment-seeking couples, N = 85 Hispanic/Latinx couples) that individuals who scored higher on the FIPPS scale also reported greater relationship satisfaction. Taken together, the FiPPS appears to be a brief and useful measure that predicts relationship satisfaction above and beyond general cognitive flexibility and perspective taking.