The Gray-breasted Martin, Progne chalybea, is a large swallow.

The nominate race P. c. chalybea breeds from Mexico through Central America south to central Brazil, and on Trinidad. P. c. macrorhamphus breeds further south in South America to central Argentina. The southern subspecies migrates north as far as Venezuela during the southern hemisphere's winter, and the nominate form also undertakes local movements after the breeding season.

The Gray-breasted Martin nests in cavities in banks and buildings, or old woodpecker holes. 2-4 eggs are laid in the lined nest, and incubated for 15-16 days, with another 22 to fledging.

Adult Gray-breasted Martins are 18 cm in length, with a forked tail and relatively broad wings, and weigh 39g. Adult males are a glossy blue-black with the grey-brown throat, breast and sides contrasting with the white lower underparts. Females are duller than the male, and juveniles have dull brown upperparts.

Gray-breasted Martins are gregarious birds which hunt for insects in flight. Their call is a gurgly chew-chew, similar to that of the closely related Caribbean Martin. The latter species is slightly larger, and has more contrasting underparts.