Weed control is a critical component of successful soybean production for almost all of the acres grown each year. Most growers use a combination of herbicides, tillage, and crop competition to control annual and perennial weeds. Beginning about 1997, soybean varieties with resistance to glyphosate became available to growers in the upper Midwest. Using glyphosate as the primary herbicide in soybeans allowed growers more flexibility in herbicide application timing, simplicity with less confusion of herbicide mixes and rates, and greater control of perennial broadleaf weeds. For these and other reasons, the adoption rate of glyphosate-resistant soybean varieties has been greater than that of any other new technology in recent history.