Similar to Tree Swallow, but smaller with shorter tail and narrower wings. Wings extend beyond tip of short tail when folded. Dark upperside contrasting with with underparts. Males have multicolored upperside, females drab-plumaged, juveniles have a dusky cheek. In flight, the white color of underside wraps onto the side of the rump.

Common. Nests in cavities and cliff crevices in open areas. Forages over open areas, usually near water.

Migratory. Breeds primarily in western North America from central Alaska and western Canada south to the Mexican highlands. Winters mostly from Mexico south to Guatemala, El Salvador, and Honduras.