Incisors (from Latin incidere, "to cut") are the first four front teeth present in heterodont mammals. They are located in the premaxilla above and on the mandible below.

In many omnivorous mammals, such as the human, they are adapted for shearing sharply. In cats, the incisors are small; biting off meat is done with the canines and the carnassials. In elephants, the upper incisors are modified into curved tusks, just as is the case with Narwhals, where normally one of them develops into a straight and twisted tusk. The incisors of rodents grow throughout life and are worn by gnawing.

Adult humans normally have eight incisors, two of each type. The types of incisor are:

Children with a full set of deciduous teeth (primary teeth) also have eight incisors, named the same way as in permanent teeth. Young children may have from zero to eight incisors depending on the stage of their tooth eruption and tooth development.

Among other animals, some other primates, cats and horses have twelve. Rodents have four, while Foxes have nine. Rabbits and hares (lagomorphs) were once considered rodents, but are distinguished by having eight—one small pair, called "peg teeth", is located directly behind the most anterior pair. Incisors are used to bite off tough foods, such as red meat.