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.