Objective This study examined the effect of a reflective interpersonal gratitude journal, a reflective‐behavioral interpersonal gratitude journal and an active control journal, on primary qualities of well‐being and depression. Method Participants (n = 192; 67.2% female) completed this 3‐month longitudinal randomized controlled design. Results Participants in the reflective‐behavioral condition experienced the greatest improvements in affect balance and reductions in depression at immediate posttest. Both gratitude interventions improved affect balance at 1 month, compared to the control. Changes in affect balance for those in the reflective‐behavioral condition were mediated by the rate at which people expressed gratitude in their existing relationships. This effect was moderated by participant's baseline depressive status. Conclusion Expressing felt gratitude to others appears to be a crucial step in deriving benefits, and these benefits may not be limited to the emotionally healthy. Given the applied popularity of gratitude interventions, understanding not only if but also how they work is essential.