The Barbary macaque (Macaca sylvanus) is a macaque species native to the Atlas Mountains of Morocco, Algeria and Tunisia, along with a small introduced population in Gibraltar. It is the type species of the genus Macaca. From the Early Pliocene to the Late Pleistocene, until around 85-40,000 years ago, it was widely distributed in Europe. Today, the Barbary macaques in Gibraltar are the only Old World monkeys in Europe. About 300 individuals live on the Rock of Gibraltar. This population appears to be stable or increasing, while the North African population is declining.

The diet of the Barbary macaque consists primarily of plants and insects. Males play an atypical role in rearing young. Because of uncertain paternity, males are integral to raising all infants. Generally, both sexes and all ages contribute in alloparental care of the young. Males live to around 25 years old while females may live up to 30 years.

The Barbary macaque is first described in scientific literature by Aristotle in the fourth century BCE work History of Animals. He writes of an ape with "arms like a man, only covered with hair", "feet [which] are exceptional in kind ... like large hands", and "a tail as small as small can be, just a sort of indication of a tail". It is likely that Galen (129–c.216) dissected the Barbary macaque in the second century CE, presuming the internal structure to be the same as a human. Such was the authority of his work, some mistakes he made were not corrected until Andreas Vesalius (1514–1564) proved otherwise over a thousand years later. The Barbary macaque was included in the grouping Simia by Conrad Gessner in his 1551 work Historia Animalium, a name which he claimed was already in use by the Greeks. Gessner's Simia was subsequently used as one of Carl Linnaeus' four primate genera when he published Systema Naturae in 1758. Linnaeus proposed the scientific name Simia sylvanus for the Barbary macaque. During the next 150 years primate taxonomy was subject to great changes and the Barbary macaque was placed in over thirty different taxa. The confusion over the use of Simia became so great that the International Commission on Zoological Nomenclature (ICZN) suppressed its use in 1929. This meant the Barbary macaque was placed in the next oldest genus assigned to it, Macaca, described by Bernard Germain de Lacépède in 1799.

The Barbary macaque is the most basal macaque species. Phylogenetic and molecular analyses show it is a sister group to all Asian macaque species. The results of a phylogenetic analysis show that the chromosomes of Barbary macaque resemble those of the rhesus macaque with the exception of chromosomes 1, 4, 9, and 16. It was also discovered that chromosome 18 in the Barbary macaque is homologous to chromosome 13 in humans.

Polymerase chain reaction studies have found Alu element insertions, small pieces of genetic code in genomes, can infer primate phylogenetic relationships. Using this method the phylogenetic relationship of ten species within the genus Macaca has been resolved, showing the Barbary macaque to be a sister group to all other macaques.

Barbary macaque fossils have been found across Europe, from the Atlantic Ocean to the Black Sea, dating from the Early Pliocene (Zanclean, 5.3 to 3.6 million years ago ) to the Late Pleistocene, assigned to various subspecies including M. s. sylvanus, M. s. pliocena and M. s. florentina. The insular dwarf M. majori endemic to Sardinia-Corsica during the Early Pleistocene, usually considered to have derived from Barbary macaque, is generally considered a distinct species. Remains from Norfolk, England, dating to the Middle Pleistocene, at 53 degrees latitude, are amongst the northernmost records of non-human primates. Archaic humans and Barbary macaque remains were found co-occurring at numerous sites. It is thought possible that humans consumed Barbary macaques. The youngest known remains of a Barbary macaque in Europe were discovered at Hunas in Bavaria, Germany, dated to 85,000–40,000 years ago. The distribution of the Barbary macaque in Europe was likely strongly influenced by climate, only extending into Northern Europe during interglacial intervals. It was restricted to more southerly regions during colder glacial phases. The disappearance of the Barbary macaque in Europe may have been caused by humans.

Fossils of the Barbary macaque are known from the Guefaït-4.2 site in Morocco, dating to around the Pliocene-Pleistocene boundary approximately 2.6 million years ago where measurements of carbon isotopes and oxygen isotopes indicate that the macaque consumed primarily the fresh fruits and leaves of C₃ plants.

The Barbary macaque has a dark pink face with a pale buff to golden brown to grey pelage and a lighter underside. The colour of mature adults changes with ages. In adults and subadults the fur on the back is variegated pale and dark which is due to banding on individual hairs. In spring to early summer, as the temperatures rise, the adult macaques moult their thick winter fur. The species shows sexual dimorphism with males larger than females. The mean head-body length is 55.7 cm (21.9 in) in females and 63.4 cm (25.0 in) in males. The boneless vestigial tail is greatly reduced compared with other macaque species and, if not absent, measures 4–22 mm (0.16–0.87 in). Males may have a more prominent tail, though data is scarce. The average body weight is 9.9–11 kg (22–24 lb) in females and 14.5–16 kg (32–35 lb) in males.