Like the pitless vipers, all crotalines are highly venomous; the Western Diamondback Rattlesnake (Crotalus atox) is responsible for the majority of snakebite deaths in North America. Pit Vipers have fangs similar to pitless vipers; the fangs are hollow and hinged, folding back against the roof of the mouth when not in use. Pit Vipers also closely resemble other vipers, having broad triangular heads and heavy builds with short, stubby tails which may or may not include a rattle.

The titular pits are between the nostril and the eye on either side of the Pit Viper's head. They contain membranes sensitive to infrared radiation; this allows the snakes to detect prey whose body temperatures are higher or lower than the surrounding environment, namely small rodents, birds and lizards. The temperature difference need not be great; fractions of a degree are enough. This adaptation serves the vipers well, as they are nocturnal animals and rely heavily on this "sixth sense". This adaptation is observed in only one other group of snakes, the boas.

In terms of length, Pit Vipers range in size from the Eyelash Viper (Bothriechis schleglii) at a maximum 50 centimetres (20 inches), to the Bushmaster (Lachesis muta) at an imposing 3.5 metres (11.5 feet). Incidentally, the Bushmaster is also the largest of all vipers, and the largest venomous snake in the New World.

Although mostly nocturnal, some species are highly active by day; one example is Trimeresurus trigonocephalus, a bright green pit viper endemic to Sri Lanka with yellow and black camouflage. The majority are active by night to avoid scorching daytime temperatures and to hunt when their preferred prey are also active. The snakes' heat-sensitive pits are also thought to aid in the location of cooler areas in which to rest.

Crotalines are characteristically ambush predator s, lying in patient wait for unsuspecting prey to wander by. At least one species, the arboreal Gloydius shedaoensis of China, is known to select a specific ambush site and return to it every year in time for the spring migration of birds. Studies have indicated that these snakes learn to improve their strike accuracy over time[1].

Many temperate species (e.g. most rattlesnakes) will congregate in sheltered areas or dens to overwinter (see hibernation), the snakes benefitting from the combined heat. In cool temperatures and whilst pregnant the vipers will also bask on sunny ledges. Some species do not mass together in this way, among them the Copperheads and Mojave Rattlesnake (Cortalus scutulatus).

Like most snakes, crotalines keep to themselves and will strike only if cornered or threatened. Smaller snakes are less likely to stand their ground than are larger specimens.

Among the oviparous (egg-laying) Pit Vipers are the Bushmaster, Calloselasma species, and some Trimeresurus species. It is believed that all egg-laying crotalines guard their eggs.

Brood sizes range from two individuals in very small species to as many as 86 in the fer-de-lance, a species among the most prolific of the live-bearing snakes. Many young crotalines have brightly coloured tails which contrast dramatically with the rest of their bodies; using worm-like movements, the young snakes may use their tails as a lure.

• Genus Agkistrodon
• Genus Atropoides
• Genus Bothriechis
• Genus Bothriopsis
• Genus Bothrocophias
• Genus Bothrops
• Genus Calloselasma
• Genus Cerrophidion
• Genus Crotalus (See Rattlesnake)
• Genus Deinagkistrodon
• Genus Ermia
• Genus Gloydius
• Genus Hypnale
• Genus Lachesis
• Genus Ophryacus
• Genus Ovophis
• Genus Porthidium
• Genus Protobothrops
• Genus Sistrurus
• Genus Triceratolepidophis
• Genus Trimeresurus
• Genus Tropidolaemus