The Barbary Ape (Macaca sylvanus) is a tail-less macaque; despite its name, it is a true monkey and not an ape. Found in the Atlas Mountains of Algeria and Morocco with a small possibly introduced population in Gibraltar, Barbary Apes are among the most well-known monkeys. Besides humans, they are the only primates that live freely in Europe.

They are yellowish-brown to grey with lighter undersides, growing to a maximum of 75 centimetres (30 inches) in length and 13 kilograms in weight. Their faces are a dark pink and their tails are vestigial. Their front limbs are longer than their hind limbs. Females are somewhat smaller than males.

Dwelling in forests of cedar, pine and oak, Barbary Apes may frequent elevations of 2,100 metres or more. They are diurnal animals, dividing their time more or less equally between arboreal and terrestrial territory. Mostly herbivorous, the monkeys feed on leaves, roots, and fruit, but will also eat insects. By day, Barbary Apes patrol a territory which may span several square kilometres; they peacefully co-exist with other primate species, sharing watering holes without incident. Barbary Apes move about energetically on all fours, occasionally rising erect on their hind limbs to survey for threats.

Barbary Apes are gregarious monkeys, forming mixed groups of several females and males; the troop of 10-30 individuals is matriarchal, with its hierarchy determined by lineage to the lead female. Unlike other macaques, the males participate in rearing the young; much time is spent playing and grooming with them. In this way, a strong social bond is formed between a male and his offspring, both the male's own and those of others in the troop. This may be a result of selectiveness on the part of the females, who seem to prefer highly parental males.

The mating season runs from November through March. After a gestation period of 147-192 days, typically one baby per female is born; twins are a rarity. The monkeys reach maturity at 3-4 years of age, and may live for 20 years or more.

The habitat of the Barbary Ape is under threat from increased logging activity; they are listed as vulnerable by the IUCN Red List. Local farmers see the monkeys as pests worthy of extermination. Once common throughout northern Africa and southern Europe, there are estimated to be just 1,200-2,000 Barbary Apes left. The last population in Europe is that of Gibraltar, approximately 100 animals. They were under the care of the British Army from 1915 to 1991; following the withdrawal of the British garrison, the government of Gibraltar took over responsibility for the apes. Due to outbreaks of disease, it has occasionally been necessary to reinforce the stock with animals from Africa.

A popular belief holds that as long as Barbary Apes exist on Gibraltar the territory will remain under British rule; it is said that during World War II Winston Churchill specifically ordered the dwindling population to be replenished for this reason.

Many of the mistaken ideas about human physiology contained in the writings of Galen are apparently due to his use of these animals, the anthropoid available to him, in dissections. A strong cultural taboo of his era prevented his performing any actual dissections of human cadavers, even in his role as physician and teacher of physicians.