As part of a cooperative agreement with the United States Department of Agriculture (USDA), the George Washington University Regulatory Studies Center produced a five-chapter report on regulatory differences between the United States (U.S.) and the European Union (EU) and their effects on agricultural production and productivity. Those chapters are published here as a working paper series with five parts. This chapter reviews how the U.S. and EU regulate water pollution from agriculture, particularly nutrient contamination from fertilizer use on crops and from the management of manure from livestock. The chapter first reviews the core environmental problem—the process by which nutrient pollution occurs and the adverse environmental and human health consequences it causes. It also provides a broad overview of the institutions and policy frameworks that shape water quality polices relevant to agriculture in the two jurisdictions and proceeds by characterizing the specific policy instruments used in the U.S. and the EU to implement these broader policy frameworks. The chapter concludes by describing the on-the-ground implementation experience and the degree to which retrospective program evaluations are performed.