Incisors are the first kind of tooth in heterodont mammals. In many herbivorous or omnivorous mammals, such as the human and the horse, they are adapted for shearing sharply. In cats, the incisors are small and do not do much; biting off meat is done with the canines and the carnassials. In elephants, the upper incisors are modified into tusks. The incisors of rodents grow throughout life and are worn by gnawing.

Humans normally have eight incisors. Among other animals, some other primates, cats and horses have twelve. The rodents have four; lagomorphs were once thought to be rodents, but are distinguished by having eight.

See also: canine tooth, molar.