The bullsnake (Pituophis catenifer sayi) is a large, nonvenomous, colubrid snake. It is a subspecies of the gopher snake (Pituophis catenifer). The bullsnake is one of the largest/longest snakes of North America and the United States, reaching lengths up to 8 ft.

The subspecific name, sayi, is in honor of American naturalist Thomas Say.
In Mexico, bullsnakes are called cincuate (/sentli/; Náhuatl: corn, /coatl/; Náhuatl: snake).
They are known as bull snakes or bullsnakes because of the deep hissing/rumbling sound they make when nervous, which can be reminiscent of a bellowing bull, as well as their overall defensive display of rearing up like a rattlesnake and rattling their tail in leaves, all of which is a bluff; the snake is not venomous, and rarely bites.

The bullsnake (Pituophis catenifer sayi) occurs throughout the Great Plains and parts of the Midwestern United States, ranging from southern Saskatchewan, and Alberta, Canada, south, into Mexico, including Nuevo León and Tamaulipas, southeast San Luis Potosi, and extreme northern Veracruz, and Hidalgo. States in the US include Colorado, Illinois, Indiana, Iowa, Kansas, Minnesota, Missouri, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Wisconsin, and Wyoming.

Adult bullsnakes average about 4 to 6 ft (1.2 to 1.8 m) in length, and specimens of up to 8 ft 4 in (2.5 m) have been recorded. The maximum record for the species is 110 in. (279 cm.). Possibly being the largest subspecies of gopher snake on average, mature specimens can have an average weight in the range of 1–1.5 kg (2.2–3.3 lb), though the heavier known specimens can attain 3.6–4.5 kg (7.9–9.9 lb), with larger specimens being quite bulky for a colubrid snake. This makes bullsnakes among the largest snakes native to Canada and the United States, although they are generally not as long as indigo snakes nor as heavy or as large in diameter as rattlesnakes. They are usually yellow, with brown, white, black, or sometimes reddish blotching. The blotching pattern is large blotches on top, three sets of spots on the sides, and bands of black on the tail. Many color variations have been found, including albinos and white varieties. A scale count is required to distinguish juvenile bullsnakes from other juvenile gopher snakes.

Bullsnakes have 33 ‒ 66 dark dorsal blotches on the body, usually 41 or more, and 9 ‒ 19 on the tail, which are often darker and bolder on the neck and tail and lighter and faded midbody. The dorsal scale rows range from 27 ‒ 37 at midbody, usually 29, 31, or 33. Bullsnakes are distinguished from other gophersnake subspecies in having large narrow rostral scale (the scale at the tip of the nose), that is higher than wide and protrudes above adjacent scales, giving the snout a relatively pointed appearance when viewed from above.

Bullsnakes are very powerful constrictors that eat small mammals, such as mice (including Peromyscus and Reithrodontomys spp.), moles, voles, rats (including Dipodomys spp.), pocket gophers, ground squirrels (including Spermophilus spp.), young rabbits and bats, as well as ground-nesting birds, birds' eggs, smaller snakes (including Crotalus spp.), lizards (including Uta spp.) and insects. Their climbing proficiency enables them to raid bird nests (and birdhouses) to eat the nestlings or sitting mother. One snake can eat five small birds within 15 minutes. Juvenile bullsnakes depend on small lizards, frogs, and baby mice.

The idea that bullsnakes occasionally eat rattlesnakes is sometimes given as a reason for humans not to harm bullsnakes when encountering them in the wild; however, a study of 1000 bullsnakes found only two had rattlesnake in their stomach contents, so this is a very rare occurrence.

Though some bullsnakes can be docile, and with some time become accustomed to handling, most are quite defensive.