Poecilia is a genus of fishes in the family Poeciliidae of the order Cyprinodontiformes. These livebearers are native to fresh, brackish and salt water in the Americas, and some species in the genus are euryhaline. A few have adapted to living in waters that contain high levels of toxic hydrogen sulfide (H2S) and a population of P. mexicana lives in caves (other populations of this species are surface-living). Micropoecilia has been proposed to be included as a subgenus of Poecilia.