Despite unprecedented recent expansion of international volunteering and service (IVS), there has been relatively little research on impacts. This paper proposes a conceptual model for impact research based on existing research evidence published in English. The model suggests that outcomes for host communities, volunteers, and sending communities vary depending on individual and institutional attributes and capacity. How institutions structure and leverage individual capacity influences who participates and how they serve, and shapes the impact of volunteer action. The conceptual model provides directions for future research.