Swallows usually breed between May and August, but this varies greatly depending on their location. At the beginning of the breeding season, males try to attract females by fanning their tails and singing as they circle above the nesting site. Although considered a monogamous bird, sometimes a male will mate with two females simultaneously.

For their part, females prefer to mate with males that show more symmetry in their wings and tail, as well as a longer tail. It has been observed that asymmetry can be the result of genetic factors and environmental stress, as well as food deficiency or parasitic infection. This would explain the fact that asymmetric individuals also show a decrease in strength and longevity. It is thus understood that females, by selecting symmetrical mates, are selecting a superior individual.

Pairs explore a good number of nesting sites before choosing. They usually return to the same breeding site year after year. Both the male and female cooperate in building the nest; first they make a small mud platform to rest on, and then they build the sides of the nest. Finally, the nest is filled with grass and feathers. It takes them about 10 days to build it.