There are currently 523 unique cases (species x site of action) of herbicide resistant weeds globally, with 269 species (154 dicots and 115 monocots). Weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 167 different herbicides. Herbicide resistant weeds have been reported in 99 crops in 72 countries. The website has 3244 registered users and 691 weed scientists have contributed new cases of herbicide resistant weeds. View Recent Additions, Site of Action Summary, or the Herbicide Classification System.