Viperidae, commonly known as vipers, is a widespread family of highly venomous snakes found across Europe, Asia, Africa, the Americas, and parts of Oceania.

The most distinctive feature of vipers is their long, hinged, retractable hollow fangs at the front of their upper jaws. When the mouth is closed, the fangs fold back against the roof of the mouth; they swing down to strike and inject venom instantly. Most vipers have thick, muscular bodies, triangular heads, vertical slit pupils, and rough, keeled scales.

Their venom is primarily hemotoxic & cytotoxic: it destroys blood cells, damages blood vessels, breaks down tissues, and causes severe bleeding & swelling. This differs from the neurotoxic venom of cobras (Elapidae).

Well-known species in this family include:

Many pit vipers also have heat-sensing pits between their eyes and nostrils, allowing them to detect warm-blooded prey in total darkness.

Unlike constrictors (Boidae/boas), vipers rely on venom to hunt; unlike cobras (Elapidae), they possess long, foldable fangs and tissue-destroying venom.