The purple martin (Progne subis) is the largest North American swallow. These aerial acrobats have speed and agility in flight, and when approaching their housing, will dive from the sky at great speeds with their wings tucked. Purple martins are a kind of swallow, of the genus Progne. Like other members of this genus, they are larger than most of the other swallows. The average length from bill to tail is 20 cm (7.9 in). Adults have a slightly forked tail. Adult males are entirely black with glossy steel blue sheen, the only swallow in North America with such coloration. Adult females are dark on top with some steel blue sheen, and lighter underparts. Subadult females look similar to adult females minus the steel blue sheen and browner on the back. Subadult males look very much like females, but solid black feathers emerge on their chest in a blotchy, random pattern as they molt to their adult plumage.
This species was first described by Linnaeus in his Systema naturae in 1758 as Hirundo subis. The species of this genus are very closely related, and some view the purple martin, gray-breasted martin, snowy-bellied martin, and southern martin, as a super-species.