There are currently 521 unique cases (species x site of action) of herbicide resistant weeds globally, with 268 species (154 dicots and 114 monocots). Weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 165 different herbicides. Herbicide resistant weeds have been reported in 98 crops in 72 countries. The website has 3211 registered users and 670 weed scientists have contributed new cases of herbicide resistant weeds. View Recent Additions, Site of Action Summary, or the Herbicide Classification System.