The common buzzard (Buteo buteo) is a medium-to-large bird of prey which has a large range. It is a member of the genus Buteo in the family Accipitridae. The species lives in most of Europe and extends its breeding range across much of the Palearctic as far as northwestern China (Tian Shan), far western Siberia and northwestern Mongolia. Over much of its range, it is a year-round resident. However, buzzards from the colder parts of the Northern Hemisphere as well as those that breed in the eastern part of their range typically migrate south for the northern winter, many journeying as far as South Africa.

The common buzzard is an opportunistic predator that can take a wide variety of prey, but it feeds mostly on small mammals, especially rodents such as voles. It typically hunts from a perch. Like most accipitrid birds of prey, it builds a nest, typically in trees in this species, and is a devoted parent to a relatively small brood of young. The common buzzard appears to be the most common diurnal raptor in Europe, as estimates of its total global population run well into the millions.

The first formal description of the common buzzard was by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Falco buteo. The genus Buteo was introduced by the French naturalist Bernard Germain de Lacépède in 1799 by tautonymy with the specific name of this species. The word buteo is Latin for a buzzard. It should not be confused with the Turkey vulture, which is sometimes called a buzzard in American English.

The Buteoninae subfamily originated from and is most diversified in the Americas, with occasional broader radiations that led to common buzzards and other Eurasian and African buzzards. The common buzzard is a member of the genus Buteo, a group of medium-sized raptors with robust bodies and broad wings. The Buteo species of Eurasia and Africa are usually commonly referred to as "buzzards" while those in the Americas are called hawks. Under current classification, the genus includes approximately 28 species, the second most diverse of all extant accipitrid genera behind only Accipiter. DNA testing shows that the common buzzard is fairly closely related to the red-tailed hawk (Buteo jamaicensis) of North America, which occupies a similar ecological niche to the buzzard in that continent. The two species may belong to the same species complex. Three buzzards in Africa are likely closely related to the common buzzard based on genetic materials, the Mountain buzzard (Buteo oreophilus), Forest buzzards (Buteo trizonatus) and the Madagascar buzzard (Buteo brachypterus), to the point where it has been questioned whether they are sufficiently distinct to qualify as full species. However, the distinctiveness of these African buzzards has generally been supported. Genetic studies have further indicated that the modern buzzards of Eurasia and Africa are a relatively young group, showing that they diverged at about 300,000 years ago. Nonetheless, fossils dating earlier than 5 million year old (the late Miocene period) showed Buteo species were present in Europe much earlier than that would imply, although it cannot be stated to a certainty that these would have been related to the extant buzzards.

Some 16 subspecies have been described in the past and up to 11 are often considered valid, although some authorities accept as few as seven. Common buzzard subspecies fall into two groups.

The western buteo group is mainly resident or short-distance migrants and includes:

The eastern vulpinus group includes:

At one time, races of the common buzzard were thought to range as far in Asia as a breeding bird well into the Himalayas and as far east as northeastern China, Russia to the Sea of Okhotsk, and all the islands of the Kurile Islands and of Japan, despite both the Himalayan and eastern birds showing a natural gap in distribution from the next nearest breeding common buzzard. However, DNA testing has revealed that the buzzards of these populations probably belong to different species. Most authorities now accept these buzzards as full species: the eastern buzzard (Buteo japonicus; with three subspecies of its own) and the Himalayan buzzard (Buteo refectus). Buzzards found on the islands of Cape Verde off of the coast of western Africa, once referred to as the subspecies B. b. bannermani, and Socotra Island off of the northern peninsula of Arabia, once referred to as the rarely recognized subspecies B. b. socotrae, are now generally thought not to belong to the common buzzard. DNA testing has indicated that these insular buzzards are actually more closely related to the long-legged buzzard (Buteo rufinus) than to the common buzzard. Subsequently, some researchers have advocated full species status for the Cape Verde population, but the placement of these buzzards is generally deemed unclear.