This report outlines the water quality challenges facing OECD countries today, presents a range of policy instruments and innovative case studies of diffuse pollution control, and concludes with an integrated policy framework to tackle diffuse water pollution.After decades of regulation and investment to reduce point source water pollution, OECD countries still face water quality challenges (e.g. eutrophication) from diffuse agricultural and urban sources of pollution, that is disperse pollution from surface runoff, soil filtration and atmospheric deposition. The relative lack of progress reflects the complexities of controlling multiple pollutants from multiple sources, their high spatial and temporal variability, associated transactions costs, and limited political acceptability of regulatory measures. This report outlines the water quality challenges facing OECD countries today, presents a range of policy instruments and innovative case studies of diffuse pollution control, and concludes with an integrated policy framework to tackle diffuse water pollution. An optimal approach will likely entail a mix of policy interventions reflecting the basic OECD principles of water quality management pollution prevention, treatment at source, the polluter pays and beneficiary pays principles, equity, and policy coherence.The OECD is an international organization that consists of 30 Member countries from the developed world that accept the principles of representative democracy and free market economy. It originated in 1948 as the Organization for European Economic Cooperation (OEEC) to help administer the Marshall Plan for the reconstruction of Europe after World War II. Later its membership was extended to non-European states, and in 1961 it was reformed into the OECD. The organization provides a forum where governments can compare policy experiences, seek answers to common problems, identify good practice and co-ordinate domestic and international policies. With active rló?