common name for a variety of nonvenomous constricting snakes. About 40 of the 64 species are true boas (family Boidae). Other boas are the Mascarene (Mascarene Islands), or split-jawed, boas (family Bolyeriidae) and dwarf boas (ground and wood boas of the family Tropidophiidae); these two families are not closely related to each other or to the true boas.

The true boas are divided into two subfamilies, Boinae and Erycinae. Boinae includes the boa constrictor (Boa constrictor), tree boas (genus Corallus), and anacondas (genus Eunectes) of the American tropics; two other genera are found on Madagascar and islands of the southwestern Pacific. Members of Boinae range from 1 metre (3.3 feet) long in some species to commonly more than 4 metres in the giant, or green, anaconda. The boa constrictor occupies a variety of habitats from coastal northern Mexico and the Lesser Antilles to Argentina; though seldom more than 3.3 metres (11 feet) long, some have grown to more than 5 metres. Several tree boas possess sizable teeth used for catching birds. An example is the 1.8-metre (6-foot) emerald tree boa (Corallus caninus) of tropical South America; the adult is green above, with a white dorsal stripe and crossbars, and yellow below. The rainbow boa (Epicrates cenchria) of Costa Rica to Argentina is not strongly patterned but is markedly iridescent. Except for the anacondas, most boines are terrestrial to strongly arboreal. The young often move from the trees to the ground as they get older and larger. Most species have labial (lip) pits with heat-sensing organs that complement their sense of smell and excellent vision. Mammals and birds are common prey, which is usually captured by a bite-grasp followed by constriction.