Chlorostilbon is a genus of hummingbird in the family Trochilidae, known as emeralds (as are some hummingbirds in the genera Amazilia and Elvira). A single species, the Blue-chinned Sapphire is variously placed in the monotypic genus Chlorestes or in Chlorostilbon. The taxonomy of the C. mellisugus superspecies is highly complex and, depending on view, includes 1-8 species. All species in this genus have straight black or black-and-red bills. The males are overall iridescent green, golden-green or bluish-green, and in some species the tail and/or throat is blue. The females have whitish-grey underparts, tail-corners and post-ocular streak.