Many contemplative traditions emphasize social benefits of contemplative practice, yet more research is needed to determine whether and how contemplative training supports social well-being. Recent advances in understanding social emotion regulation (SER) highlight the importance of both intrapersonal and interpersonal strategies, and offer exciting new approaches and methods for investigating social effects of contemplative practice. The proposed project brings these new approaches and methods from SER research to bear on the study of mindful compassion training (MCT), examining effects of MCT on SER processes during day-to-day social interactions. Specifically, smartphone-based surveys will be used to test whether and how MCT promotes personal and social well-being via changes in SER during real-life social interactions. Eighty meditation-naïve participants will be randomly assigned to MCT or a wait-list control. Compared with controls, I expect MCT will increase interaction-based compassion and alter SER strategy deployment along three key SER dimensions, namely intrapersonal versus interpersonal, intrinsic versus extrinsic, and response-dependence versus response-independence. These key SER dimensions represent candidate mechanisms to explain social effects of mindfulness and compassion training broadly, such that the proposed project has strong potential to inform current understanding and motivate future research on social outcomes of contemplative training.