The red-tailed hawk (Buteo jamaicensis) is a bird of prey and one of the most common hawks in North America. In the United States, it is one of three species colloquially known as the "chickenhawk". The red-tailed hawk breeds throughout most of the continent, from western Alaska and northern Canada to as far south as Panama and the West Indies. The red-tailed hawk occupies a wide range of habitats and altitudes including deserts, grasslands, coniferous and deciduous forests, agricultural fields and urban areas. It is absent in areas of unbroken forest and in the high arctic. It is legally protected in Canada, Mexico and the United States by the Migratory Bird Treaty Act.

The red-tailed hawk is one of the largest members of the genus Buteo in North America, typically weighing from 690 to 1,600 g (1.5 to 3.5 lb) and measuring 45–65 cm (18–26 in) in length, with a wingspan from 110–145 cm (43–57 in). Females are about 25% heavier than males. It has a stocky body with broad wings, and can be distinguished from other North American hawks by the eponymous tail, which is uniformly brick-red above and light buff-orange below. The species feeds on a wide range of small animals such as rodents, birds, and reptiles. Pairs stay together for life, taking a new mate only when the original mate dies. The pair constructs a stick nest in a high tree, in which a clutch of one to three eggs is laid.

The 14 recognized subspecies vary in appearance and range. The subspecies Harlan's hawk (B. j. harlani) is sometimes considered a separate species (B. harlani). Because they are so common and easily trained as capable hunters, the majority of hawks captured for falconry in the United States are red-tailed hawks. The feathers and other parts of the red-tailed hawk are considered sacred to many American indigenous people.

The red-tailed hawk was scientifically described in 1788 by German naturalist Johann Friedrich Gmelin under the name Falco jamaicensis. Gmelin based his description on the "cream-coloured buzzard" described in 1781 by John Latham in his A General Synopsis of Birds, based on a specimen from Jamaica that a friend sent to him. The red-tailed hawk is one of 28 species in the genus Buteo, which was named by French naturalist Bernard Germain de Lacépède in 1799. Members of the genus Buteo are medium-sized raptors with robust bodies and broad wings. They are known as buzzards in Europe, but as hawks in North America.

The genus name Buteo is derived from the Latin būteō meaning 'buzzard'. The specific name jamaicensis refers to the island of Jamaica, which derives from the Taíno word Xaymaca meaning 'land of woods and water'. "Red-tailed hawk" is the official English common name designated by the International Ornithologists' Union (IOU). In the United States, the red-tailed hawk is one of three species colloquially known as the "chickenhawk," though it rarely preys on standard-sized chickens.

There are at least 14 recognized subspecies of Buteo jamaicensis, which vary in range and in coloration: The subspecies Harlan's hawk (B. j. harlani) is sometimes considered a separate species (B. harlani).

The red-tailed hawk is sexually dimorphic in size, as females are up to 25% larger than males. As is typical in large raptors, frequently reported mean body mass for red-tailed hawks is somewhat higher than expansive research reveals. Part of this weight is highly seasonally variable and due to clinal variation, male red-tailed hawks may weigh from 690 to 1,300 g (1.52 to 2.87 lb) and females between 900 and 2,000 g (2.0 and 4.4 lb). However, research from nine studies occurring at migration sites in the United States and two breeding studies, one from the smallest race in Puerto Rico, the other from larger races in Wisconsin, show that males weigh a mean of 837 g (1.845 lb) and females weigh a mean of 1,040.7 g (2.294 lb), about 15% lighter than prior species-wide published weights. The heaviest surveyed weights came from migrants in Cape May, New Jersey, where females weighed a mean of 1,278 g (2.818 lb), males a mean of 990.8 g (2.184 lb). The lightest were from the breeding population in forest openings of Puerto Rico, where the females and males weighed an average of 1,023 g (2.255 lb) and 795 g (1.753 lb), respectively, also the highest size sexual dimorphism in the species. Size variation in body mass reveals that the red-tailed hawks typically vary only a modest amount; racial variation in average weights of great horned owls show that mean body mass is nearly twice (the heaviest race is about 36% heavier than the lightest known race on average) as variable as that of the hawk (where the heaviest race is only just over 18% heavier on average than the lightest). Males can reportedly measure 45 to 60 cm (18 to 24 in) in total length, females measuring 48 to 65 cm (19 to 26 in) long. The wingspan can range from 105 to 141 cm (41 to 56 in) and, in the standard scientific method of measuring wing size, the wing chord is 325.1–444.5 mm (12.80–17.50 in) long. The tail measures 188 to 258.7 mm (7.40 to 10.19 in) in length. The middle toe (excluding talon) can range from 38.3 to 53.8 mm (1.51 to 2.12 in), with the hallux-claw (the talon of the rear toe, which has evolved to be the largest in accipitrids) measuring from 24.1 to 33.6 mm (0.95 to 1.32 in) in length.

Red-tailed hawk plumage can be variable, depending on the subspecies and the region. These color variations are morphs, and are not related to molting. The western North American population, B. j. calurus, is the most variable subspecies and has three color morphs: light, dark, and intermediate or rufus. The dark and intermediate morphs constitute 10–20% of the population.