The rough-legged buzzard (Europe) or rough-legged hawk (North America) (Buteo lagopus) is a medium-large bird of prey. It is found in arctic and subarctic regions of North America, Europe, and Asia during the breeding season, and migrates south for the winter. Historically, it was also known as "rough-legged falcon" in such works as John James Audubon's The Birds of America.

Nests are typically located on cliffs, bluffs or in trees. The clutch sizes are variable with food availability, but usually three to five eggs are laid. They hunt over open land, feeding primarily on small mammals, mainly lemmings and voles. Along with the kestrels, kites, and osprey, this is one of the few birds of prey to hover regularly.

This fairly large raptorial species is 46–68 cm (18–27 in) with wingspan ranging from 120 to 153 cm (47 to 60 in). Individuals can weigh from 600 to 1,660 g (1.32 to 3.66 lb) with females typically being larger and heavier than males. Weights appear to increase from summer to winter in adults, going from an average of 822 to 1,027 g (1.812 to 2.264 lb) in males and from 1,080 to 1,278 g (2.381 to 2.818 lb) in females. Among the members of the genus Buteo, it is sixth heaviest, the fifth longest, and the fourth longest winged. Among standard measurements in adults, the wing chord is 37.2–48.3 cm (14.6–19.0 in), the tail is 18.6–25.5 cm (7.3–10.0 in), culmen is 3.2–4.5 cm (1.3–1.8 in) and the tarsus is 5.8–7.8 cm (2.3–3.1 in). The plumage is predominantly brown and white, and often shows a high degree of speckling. A broad brown chest-band is present in most plumages and a square dark carpal patch contrasting with the white under-wing is an easily identifiable characteristic in light morph individuals. A wide variety of plumage patterns are exhibited in light vs. dark morphs, males vs. females, and adults vs. juveniles. Extensive field experience is required to distinguish between certain plumage variations. Compared to its more common Palearctic and Nearctic cousins, the common buzzard (Buteo buteo) and the red-tailed hawk (Buteo jamaicensis), it is slightly larger, though may be outweighed by the latter.

Its legs are feathered, though not the toes, as an adaptation to cold in its Arctic home range. Its scientific name reflects this feature, as lagopus means "hare-foot". Its talons are relatively small, reflecting their preferred choice of prey.

Distinguishing characteristics in all plumages include long white tail feathers with one or more dark subterminal bands. The wing tips are long enough to reach or extend past the tail when it is perched. The common buzzard can be similar-looking, with a similar long-tailed shape and can be notoriously variable in plumage; rough-legged is longer-winged and more eagle-like in appearance. The red-tailed hawk is chunkier-looking and differs in its darker head, broader, shorter wings, barring on the wings and the tail, dark leading edge to the wings (rather than black wrist patch) and has no white base to the tail. The ferruginous hawk is larger, with a bigger, more prominent bill and has a whitish comma at the wrist and all-pale tail.

It is the only raptor of its size (other than the very different-looking osprey) to regularly hover over one spot, by beating its wings quickly.

The rough-legged buzzard is a member of the genus Buteo, a group of moderately large raptors exhibiting broad wings, short tails and wide robust bodies. This genus is known as buzzards in Europe but referred to as hawks in North America. The generic name Buteo is the Latin name of the common buzzard (Buteo buteo), and the specific epithet lagopus is derived from Ancient Greek lago (λαγως), meaning "hare", and pous (πους), "foot".

Four subspecies of Buteo lagopus are accepted: