Russell's viper (Daboia russelii) is a highly venomous snake in the family Viperidae native to South Asia.

English naturalist George Shaw—with illustrator Frederick Polydore Nodder—in The Naturalist's Miscellany: Or, Coloured Figures Of Natural Objects; Drawn and Described Immediately From Nature formally described the species in 1797 as Coluber russelii, from a specimen presented to the British Museum by Scottish herpetologist Patrick Russell.

[2] Russell had written of the species in his 1796 work An account of Indian serpents, collected on the coast of Coromandel, confirming its highly venomous nature by experimenting on chickens and dogs.

[3] Analysis of morphological and mitochondrial DNA data shows that the eastern subspecies of D. russelii should be considered a separate species, Daboia siamensis.

McDiarmid et al. (1999) are among those who favor the original misspelling, citing Article 32c (ii) of the International Code of Zoological Nomenclature.

The two maxillary bones support at least two, and at the most five or six, pairs of fangs at a time: the first are active and the rest replacements.

The head has a pair of distinct dark patches, one on each temple, together with a pinkish, salmon, or brownish V or X marking that forms an apex towards the snout.

[18] The following dimensions for a "fair-sized adult specimen" were reported in 1937:[19] Russell's viper is found in India, Sri Lanka, Bangladesh, Nepal, and Pakistan.

[5] This species is often found in highly urbanized areas and settlements in the countryside, the attraction being the rodents commensal with man.

D. russelii does not associate as closely with human habitation as Naja and Bungarus species (cobras and kraits).

[5] When threatened, they form a series of S-loops, raise the first third of the body, and produce a hiss that is supposedly louder than that of any other snake.

If provoked even more, they resort to striking and can exert so much force that large individuals can lift off the ground in the process.

[21][22] The identity of this sensor is not certain, but the nerve endings in the supranasal sac of these snakes resemble those found in other heat-sensitive organs.

[18] Mating generally occurs early in the year, although pregnant females may be found at any time.

[5] Russell's viper feeds primarily on rodents, although it will also eat small reptiles, land crabs, scorpions, and other arthropods.

[17] Some herpetologists believe, because D. russelii is so successful as a species and has such a fearful reputation within its natural environment, another snake has come to mimic its appearance.

Superficially, the rough-scaled sand boa Eryx conicus has a color pattern that often looks like that of D. russelii, though it is completely harmless.

[29] Envenomation symptoms begin with pain at the site of the bite, immediately followed by swelling of the affected extremity.

Bleeding is a common symptom, especially from the gums and in the urine, and sputum may show signs of blood within 20 minutes after the bite.

Discoloration may occur throughout the swollen area as red blood cells and plasma leak into muscle tissue.

[17] A study in The Lancet showed that out of a sample of people who survived bites by D. russelii, 29% suffered severe damage to their pituitary glands, which later caused hypopituitarism.

[31][32] In India, the Haffkine Institute prepares a polyvalent antivenom that is used to treat bites from this species.

[17] In late 2016, a new antivenom had been developed by the Costa Rican Clodomiro Picado Institute and clinical trials were started in Sri Lanka.

[33] Because this venom is so effective at inducing thrombosis, it has been incorporated into an in vitro diagnostic test for blood clotting that is widely used in hospital laboratories.