There are currently 534 unique cases (species x site of action) of herbicide resistant weeds globally, with 273 species (156 dicots and 117 monocots). Weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 168 different herbicides. Herbicide resistant weeds have been reported in 101 crops in 75 countries. The website has 3358 registered users and 720 weed scientists have contributed new cases of herbicide resistant weeds. View Recent Additions, Site of Action Summary, or the Herbicide Classification System.