At the 1990 meeting of the Weed Science Society of America (WSSA) in Montreal a Symposium titled “Pesticide Transport to Groundwater: Perspectives and Field Methodology” was Chaired by Thanh H. Dao. That symposium made it clear that simulation modeling is being used more and more to integrate the field test data generated by pesticide companies as part of the environmental impact assessment required for pesticide registration with the Environmental Protection Agency (EPA). At the Soil Aspects Section Business Meeting it was decided that a Symposium on the state of the art of this technology would be timely and the authors agreed to organize it.