Romantic relationships among young adults are rich with ambiguity and without a clear, universal progression emphasizing the need for active decision making. Lack of active decision making in romantic relationships can lead to increases in constraints (e.g. pregnancy, shared living space or finances) that promote the continuation of relationships that would have otherwise ended, leading to increased risk of relationship distress. Because there is no available assessment of thoughtfulness regarding relationship decisions, the authors of the present studies report data on the development of one such scale, the Relationship Deciding Scale (RDS). Study 1 (N = 995) reveals the factor structure of the RDS and provides reliability data for the emergent subscales. In Study 2 (N = 963), the obtained three-factor structure (Relationship Confidence, Knowledge of Warning Signs, and Deciding) is tested via confirmatory factor analysis, demonstrates convergent and discriminant validity, and is shown to predict relationship characteristics 14 weeks later. Study 3 (N = 805) shows the sensitivity of the three factors to change through examination of the influence of a semester-long intervention targeted at increasing decision making in relationships. Use of this scale for identifying and intervening with couples or individuals who lack active decision making in relationships may decrease their risk for future relationship distress. (Contains 2 figures, 5 tables, and 1 footnote.)