The common raven was one of the many species originally described by Linnaeus in his 18th century work, Systema Naturae, and it still bears its original name of Corvus corax. It is the type species of the genus Corvus, derived from the Latin word for "raven". The specific epithet, corax/κοραξ, is the Ancient Greek word for "raven" or "crow".
The modern English word raven has cognates in all other Germanic languages, including Old Norse (and subsequently modern Icelandic) hrafn and Old High German (h)raban, all which descend from Proto-Germanic *khrabanas. An old Scottish word corby or corbie, akin to the French corbeau, has been used for both this bird and the carrion crow. Obsolete collective nouns for a group of ravens (or at least the common raven) include "unkindness" and "conspiracy". In practice, most English-speakers use the more generic "flock".
The closest relatives of the common raven are the brown-necked raven (C. ruficollis), the pied crow (C. albus) of Africa, and the Chihuahuan raven (C. cryptoleucus) of the North American southwest. While some authorities have recognized as many as 11 subspecies, others recognize only eight:
|C. c. corax
||From Europe eastwards to Lake Baikal, south to the Caucasus region and northern Iran
||It has a relatively short, arched bill. The population in southwestern Europe (including the Balearic Islands, Corsica and Sardinia) has an even more arched bill and shorter wings than "typical" nominate, leading some authorities to recognize it as a separate subspecies, C. c. hispanus.
|C. c. varius
||Iceland and the Faroe Islands
||It is less glossy than C. c. principalis or nominate corax, is intermediate in size, and the bases of its neck feathers are whitish (not visible at a distance). An extinct white and black color morph found only on the Faroes is known as the pied raven.
|C. c. subcorax
||From Greece eastwards to northwestern India, Central Asia and western China, though not the Himalayan region
||It is larger than the nominate form, but has relatively short throat feathers (hackles). Its plumage is generally all black, though its neck and breast have a brownish tone similar to that of the brown-necked raven; this is more evident when the plumage is worn. The bases of its neck feathers, although somewhat variable in colour, are often almost whitish.
The name C. c. laurencei (also spelt lawrencii or laurencii) is sometimes used instead of C. c. subcorax. It is based on the population from Sindh described by Hume in 1873 and is sometimes preferred since the type specimen of subcorax collected by Nikolai Severtzov is possibly a brown-necked raven.
The population restricted to the Sindh district of Pakistan and adjoining regions of northwestern India is sometimes known as the Punjab raven.
|C. c. tingitanus
||North Africa and the Canary Islands
||It is the smallest subspecies, with the shortest throat hackles and a distinctly oily plumage gloss. Its bill is short but markedly stout, and the culmen is strongly arched. Canary Islands ravens are browner than the North African ravens, leading some authorities to treat them as separate subspecies, with the latter maintaining the name C. c. tingitanus and the former known as C. c. canariensis.
|C. c. tibetanus
||It is the largest and glossiest subspecies, with the longest throat hackles. Its bill is large but less imposing than that of C. c. principalis, and the bases of its neck feathers are grey.
|C. c. kamtschaticus
||Intergrades into the nominate subspecies in the Baikal region. It is intermediate in size between C. c. principalis and C. c. corax and has a distinctly larger and thicker bill than does the nominate race.
|C. c. principalis, the northern raven
||Northern North America and Greenland
||It has a large body and the largest bill, its plumage is strongly glossed, and its throat hackles are well developed.
|C. c. sinuatus, the western raven
||South-central North America and Central America
||It is smaller, with a smaller and narrower bill than C. c. principalis. Populations in far southwestern USA and northwestern Mexico (including the Revillagigedo Islands) are the smallest in North America. They are sometimes included in C. c. sinuatus, while other authorities recognize them as a distinct subspecies, C. c. clarionensis, the southwestern raven.
The common raven evolved in the Old World and crossed the Bering land bridge into North America. Recent genetic studies, which examined the DNA of common ravens from across the world, have determined that the birds fall into at least two clades: a California clade, found only in the southwestern United States, and a Holarctic clade, found across the rest of the Northern Hemisphere. Birds from both clades look alike, but the groups are genetically distinct and began to diverge about two million years ago.
The findings indicate that based on mitochondrial DNA, common ravens from the rest of the United States are more closely related to those in Europe and Asia than to those in the California clade, and that common ravens in the California clade are more closely related to the Chihuahuan raven (C. cryptoleucus) than to those in the Holarctic clade. Ravens in the Holarctic clade are more closely related to the pied crow (C. albus) than they are to the California clade. Thus, the common raven species as traditionally delimited is considered to be paraphyletic.
One explanation for these genetic findings is that common ravens settled in California at least two million years ago and became separated from their relatives in Europe and Asia during an ice age. One million years ago, a group from the California clade evolved into a new species, the Chihuahuan raven. Other members of the Holarctic clade arrived later in a separate migration from Asia, perhaps at the same time as humans.
A 2011 study suggested that there are no restrictions on gene flow between the Californian and Holarctic common raven groups, and that the lineages can remerge, effectively reversing a potential speciation.
A recent study of raven mitochondrial DNA showed that the isolated population from the Canary Islands is distinct from other populations. The study did not include any individuals from the North African population, and its position is therefore unclear, though its morphology is very close to the population of the Canaries (to the extent that the two are often considered part of a single subspecies).