This volume addresses the use of urban wastewater in agriculture, a centuries old practice that is receiving renewed attention with the increasing scarcity of fresh water resources faced by many arid and semi-arid countries. Driven by rapid urbanization and growing wastewater volumes, wastewater is widely used as a low cost alternative to conventional irrigation water, and generates considerable value in urban and peri-urban agriculture despite the health and environmental risks associated with this practice. Though pervasive, this practice is largely unregulated in poor countries, and the health and environmental costs and benefits are unknown or unacknowledged. Existing options to treat wastewater for reuse are often beyond the financial means of municipalities and farmers in these countries.