The Martins and Swallows (Hirundinidae) are a group of 88 species of passerine birds which are characterised by their adaptation to aerial feeding. This family comprises two subfamilies: Pseudochelidoninae (the river martins of the genus Pseudochelidon) and Hirundininae (all other swallows and martins). Within the Hirundiniae, the name "martin" tends to be used for the squarer-tailed species, and the name "swallow" for the more fork-tailed species; however, there is no scientific distinction between these two groups.

The swallows have a cosmopolitan distribution across the world and breed on all the continents except Antarctica. It is believed that this family originated in Africa as hole-nesters; Africa still has the greatest diversity of species. They also occur on a number of oceanic islands.

The swallows and martins have an evolutionary conservative body shape which is similar across the family but is unlike that of other passerines. Swallows have adapted to hunting insects on the wing by developing a slender streamlined body and long pointed wings, which allow great maneuverability and endurance, as well as frequent periods of gliding. Their body shape allows for very efficient flight, which costs 50-75 % less for swallows than equivalent passerines of the same size. Swallows usually forage at around 30–40 km/h, although they are capable of reaching speeds of between 50–65 km/h when traveling. Like the unrelated swifts and nightjars, which hunt in a similar way, they have short bills, but strong jaws and a wide gape.

Swallows are tolerated by humans because of their beneficial role as insect-eaters, and some species have readily adapted to nesting in and around human habitation. The Barn Swallow and House Martin now rarely use natural sites. The Purple Martin is also actively encouraged by people to nest around humans and elaborate nest boxes are erected. Enough artificial nesting sites have been created that the Purple Martin now seldom nests in natural cavities in the eastern part of its range.

Because of the long human experience with these conspicuous species, many myths and legends have arisen as a consequence, particularly relating to the Barn Swallow. The Roman historian Pliny the Elder described a use of painted swallows to deliver a report of the winning horses at a race. During the nineteenth century, Jean Desbouvrie attempted to tame swallows and train them for use as messenger birds, as an alternative to war pigeons.