Herbicides are transported through subsurface drainage to surface waters from corn-growing areas of the USA and Canada. Herbicide losses are highly variable, ranging between 0.01 to 10 g/ha. The magnitude of herbicide loss results from precipitation patterns, herbicide-soil interactions, and farming practices. This report reviews existing literature and presents new research concerning effects of farming practices on herbicide losses in drainage water. Conservation tillage practices which increase infiltration tend to increase herbicide losses. Increasing intensity of drainage and increased frequency and rate of herbicide use also increase herbicide losses. Banding lowers the application rate and reduces annual losses and average concentrations of atrazine compared to broadcast applications. Metolachlor losses were reduced by banding, but the effect was only statistically significant in continuous corn systems.