Religion and spirituality are vital aspects of many people’s lives both in the United States and across the globe. Although many constructs and measures exist to describe and assess the experience of pursuing the sacred, the complexity of religious and spiritual experience leads to mixed results in relation to well-being and psychopathological traits. However, in broad terms, the relationship appears positive. Over the past 30 years the need for more refined and useful approaches to the study of religious and spiritual behavior has been repeatedly acknowledged. Although authors wisely caution development of further measures without due cause, extant constructs and measures do not provide clear and consistent results for understanding the influence of one’s relationships to religion and spirituality upon behaviors of clinical interest. The present project drew from the functional contextual concept of psychological flexibility, which provides clarity to understanding the encouragement and maintenance of psychological well-being. A new construct of religious and psychological flexibility is explicated as a functional approach to understanding religious and spiritual behavior in a manner that is useful in research and clinical settings alike. The development and evaluation of the Measure of Religious and Spiritual Flexibility (MRSF) is described. The MRSF evidenced adequate internal …