Swallows and hirundidae are a family of Passeriformes from all continents except Antarctica. They are very suitable for air feeding and have a unique appearance. Swallow is commonly used as a synonym for swallow in Europe. There are about 83 species in 19 genera, and the most diversity is found in Africa, which is also considered to be the place where they evolved as hole nesting animals. They also happen on many ocean islands. Many European and North American species are long-distance immigrants. In contrast, swallows in the West and South Africa are non migratory.

The family includes two subfamilies: pseudopodinae and hirundinae (all other swallows and Martins). In the old world, the square tailed species tended to use the name Martin, while the fork tailed species tended to swallow the name. However, there was no scientific difference between the two groups. In the new world, "Martin" is reserved for members of the Progne genus. These two systems led sardine to be called "shore swallow" in the new world.

Swallows and Martins have evolutionarily conservative bodies, similar in the whole evolutionary branch, but different from other Passeriformes. Swallows adapt to insect hunting by forming slender, streamlined bodies and long pointed wings. These wings have excellent mobility and endurance, and can often glide. They can fly very efficiently; in flight, the metabolic rate of swallows is 49 – 72% lower than that of birds of the same size.

The sardine bill is typical, short and wide for families.

Swallows have two central recesses in each eye, making their lateral and frontal vision clear and helping to track prey. Their eyes are also longer, and their length is almost equal to their width. Long eyes increase vision without competing with the brain for space inside the head. The eyes of swallows are similar to those of raptors.

Just as unrelated swifts and nighthawks hunt in similar ways, their bills are short, but their jaws are strong and wide. They are about 10 – 24 cm (3.9 – 9.4 in) long and weigh about 10 – 60 g (0.35 – 2.12 oz). The wings are long and pointed, with nine main feathers. The tail has 12 feathers and may be deeply branched, with some sunken or square ends. Long tails increase operability and can also be used as a sexual decoration, as the male tail is usually longer. In swallows, the male's tail is 18% longer than the female's, and the female chooses a mate based on the length of the tail.

The legs are short, and the feet of the feet are suitable for perching rather than walking, because the front toes are partially engaged at the bottom. Swallows can walk, or even run, but they stumble. His leg muscles are stronger than those of other swallows. There are other features of the Martin river that distinguish them from other swallows. The structure of syrinx is very different between the two subfamilies. In most swallows, the legs and feet of the thighs are dark brown or black, but in hippopotamus, the thighs are orange red, and the legs and feet are pink.

The most common Canary feathers are bright dark blue or green on the top and flat or striped at the bottom, usually white or golden brown. In dry or mountainous areas, the species that usually dig or live is usually matte Brown (such as sardine and C). There is a limited or no gender difference in gender, and the longer outer tail feathers of adult males may be the most common difference.

The chicks hatch naked with their eyes closed. Juveniles with adults usually appear in the rigid form of adults.