In this chapter, we examine the intersections of positive psychology (PP) and religiousness/spirituality (R/S) in close relationships. Specifically, within Mahoney’s (J Marriage Fam 72:805–827, 2010) relational spirituality framework, we focus on the maintenance stage of healthy relationships and explore helpful roles that R/S can play for diverse types of couples and families. We briefly summarize extensive evidence that global markers of R/S (e.g., religious service attendance) are associated with relational well-being. We also highlight that global markers of R/S confound relatively commonplace positive religious/spiritual processes with less common but potentially toxic manifestations of R/S. We then delve into four specific religious/spiritual strengths that are empirically tied to better relational functioning: sanctification, spiritual intimacy, prayer for partner, and positive religious/spiritual coping. Next, we offer guidelines consistent with available scientific research that religious leaders, chaplains, couple and family educators, and psychotherapists might consider when working in community or clinical settings. Finally, we suggest ways to advance science and practice on the roles of R/S, for better and worse, within intimate and family relationships.