The 70-item Unified Flexibility and Mindfulness (UFM) scale was created to assess the 14 components of the UFM model—a conceptual framework bridging the mindfulness and acceptance and commitment therapy literatures, integrating forms of mindfulness into a stepwise process model. The UFM model posits that engaging mindful lenses to sustain an open-hearted awareness of the present moment (i.e., describing, observing, and mindful awareness) will create space to allow individuals to decenter from difficult thoughts and feelings (i.e., acceptance, gently experiencing difficult thoughts/feelings, and maintaining a broader perspective), enabling them to engage in more informed/ethical/value-driven behavior on a day-to-day basis (maintaining contact with deeper values, continuing to take steps toward deeper goals even in the midst of difficult experiences), thereby promoting well-being. The 70-item UFM scale was developed in a sample of 2742 online respondents using exploratory factor analyses (EFAs) and item response theory (IRT) analyses to optimize the subscales. A shorter 28-item UFM scale was also developed and validated for use in contexts that could not accommodate the longer scale. The UFM subscales demonstrated robust levels of internal consistency that generalized to 22 demographic groups and a factor structure that cross-replicated using EFAs and confirmatory factor analyses (CFAs) in separate sample halves. Extending this psychometric validation, the UFM subscales demonstrated measurement invariance across gender, age, and meditation groups. Finally, the UFM subscales demonstrated discriminant validity with one another and real-world criterion validity by showing marked differences across the 14 dimensions between individuals practicing Buddhist meditation and nonmeditators.