Vampire bats are bats that feed on blood. There are only three bat species that feed on blood: The Common Vampire Bat, Desmodus rotundus, the Hairy-legged Vampire Bat, Dyphilla ecaudata, and the White-winged Vampire Bat, Diaemus youngi. All three species are native to the Americas, ranging from Mexico to Brazil, Chile, and Argentina.

The three species are quite different from each other, and are therefore placed within different genera (no other species are currently classified in any of the three genera concerned). But they are related. In older literature, the three genera are placed within a family, Desmodontidae, but this is now regarded as unhelpful, as it hides the similarities the vampire bats have with other members of the American leaf-nosed bat family, Phyllostomidae. They are therefore now grouped as a subfamily, the Desmodontinae within the Phyllostomidae.

The fact that the three known species of vampire bat all seem more similar to one another than any of them is to any other species suggests that sanguivory (feeding on blood) only evolved once, and that all three species share a common ancestor.

Unlike fruit-eating bats, the vampire bats have a short, conical muzzle without a nose leaf. Instead they have naked pads with U-shaped grooves at the tip. They have small ears and a short tail membrane. Their front teeth are specialised for cutting and their back teeth are much smaller than in other bats. Their digestive systems are also specialised for their liquid diet. The saliva of vampire bats contains a substance, draculin, which prevents the victim's blood from clotting.

Vampire bats tend to live in almost completely dark places, such as caves, old wells, hollow trees, and buildings. Colonies can range from a single individual to thousands. They often roost with other species of bat. They come out only when it is fully dark. Like fruit-eating bats, and unlike insectivorous and fish-eating bats, they only emit low-energy sound pulses.

They need blood at least once every few days to survive. If they can't get blood, they'll approach another bat whilst roosting, asking for a blood 'transfusion'. The blood is exchanged mouth-to-mouth in a motion that looks very much like kissing. Vampire bats also can run and walk.

In a study which appeared in the January 10, 2003 issue of Stroke: Journal of the American Heart Association, a genetically engineered drug called desmoteplase based on the spit of Desmodus rotundus was shown to improve stroke patients.

For folklore about humans or near-humans who feed on blood, see vampire