Aminopyralid is a recently discovered herbicide being developed by Dow AgroSciences for rangeland and pasture vegetation management systems. Other anticipated use-sites for this herbicide include Conservation Reserve Program acres, non-cropland, and natural areas. Aminopyralid is a pyridine carboxylic acid that is formulated as a 240 g acid equivalent (ae)/liter product and has an auxinic mode of action. Aminopyralid has low acute and chronic toxicity (practically nontoxic) to mammals, birds, fish, and aquatic invertebrates, with no evidence of teratogenicity, mutagenicity, carcinogenicity, or adverse endocrine or reproductive effects. Aminopyralid is only slightly toxic to algae and aquatic vascular plants and substantially below US EPA's levels of concern for adverse effects on these organisms. Aminopyralid has a favorable environmental fate because of moderate degradation in soil (t1/2 = 34 d) and rapid photolysis in aquatic habitats (t1/2 = 0.6 d) with CO2 and NH3 as the only metabolites. Aminopyralid provides preemergence and postemergence control of many broadleaf noxious and invasive plants with little to no injury to most rangeland and pasture grasses. Aminopyralid is effective at rates between 53 and 120 g ae/ha, which is about 1/4 to 1/20 of the use rates for currently registered rangeland and pasture herbicides including, 2,4-D, picloram, clopyralid, triclopyr, and dicamba. Undesirable plants in the Acroptilon, Ambrosia, Carduus, Centaurea, Cirsium, Solanum, and Vernonia genera are among those controlled by aminopyralid.