Pollution takes an enormous toll, both in terms of impact on healthy lives and environmental degradation—to the extent that it jeopardizes progress made in poverty alleviation. While the 2001 World Bank environment strategy calls for mainstreaming environmental concerns into country development programs, the 2012 World Bank Group environmental strategy, Toward a Green, Clean, and Resilient World for All, explicitly defines a “clean world” as a strategic objective—a world with “low pollution and low emission.” The World Bank Group approved a total of 3,870 projects, accounting for approximately US$297 billion in commitments that are pollution-relevant over the last 12 years, FY2004-15. To date, the effectiveness of these interventions has not yet been evaluated. This study will be the first stock-taking exercise focusing on those pollution phenomena that affect poor countries the most, that is, air and water pollution, and waste.