Objective: Following a major life crisis, people may simultaneously report both significant distress and positive change or posttraumatic growth (PTG; Calhoun & Tedeschi, 2006). Accumulating evidence has suggested that in close relationships, PTG can be mutual, wherein 1 person’s PTG is positively correlated with others’ PTG (e.g., Manne et al., 2004). However, the mechanism by which mutual growth occurs is unclear. We suggest that an interpersonal process mediates mutual PTG between partners, and we draw from the social psychology and relationship science literatures to suggest that the interpersonal process of responsiveness may explain people’s correlated PTG following trauma. Method: Married couples (61 at Time 1; 48 at Time 2) whose homes had been severely damaged by flooding completed measures of PTG, responsiveness to partners, and perceptions of partners’ responsiveness at 2 time points, 6 months apart. Results: Findings did not consistently replicate a direct link between actors’ and partners’ PTG. Results did support an interpersonal process by which actors’ PTG predicted their greater responsiveness to partners; partners perceived actors’ greater responsiveness, which predicted partners’ greater PTG. Further, this interpersonal pathway was independent of known intrapsychic predictors of PTG, social support, and relationship quality. Conclusion: These results suggest that close relationships may play an important role in fostering PTG and are the first to outline an interpersonal process by which people experience mutual growth and personal growth can be passed from 1 person to another.