The identification of relationship-relevant individual differences is central to elucidating how relationship experiences differentially impact individuals’ health. To this end, we highlight the utility of studying the influence of individual differences on physiological outcomes (e.g., cortisol reactivity and recovery) in the context of normative relationship transitions. We argue that relationship transitions, such as falling in love and the process of committing to marry one's partner, amplify the influence of individual differences on relationship processes and, by extension, on physiological outcomes. Two such individual differences are highlighted—namely, relationship-focused processing and dependence—and suggestions for future work are provided.