猴，俗称猴子，粤:马骝，是三种类人猿灵长目动物的其中两种的成员。这三种类包括新世界猴、旧世界猴和猿。新世界猴被分类在小目——阔鼻小目（Platyrrhini）下，旧世界猴（猴总科 Cercopithecoidea）则是狭鼻小目（Catarrhini）的一部分，这个目也包括猿。因此科学上来说，猴并没有形成一个「自然群组」，旧世界猴实际上也接近猿多过新世界猴。现存并所知的有264种猴。另外由于猿类似猴，黑猩猩、长臂猿等在非正式场合也常被称为猴，但生物学家并不认为牠们是猴。还有，有些猴种类的名字里有「猿」，因为牠们是并系群，猴没有任何显著的特征，因为牠们的特征都是源于类人猿和猿。

In his Systema Naturae of 1758, Carolus Linnaeus divided the Order Primates into four genera: Homo, Simia, Lemur, and Vespertilio. His Vespertilio included all bats, and has since been moved from Primates to Chiroptera. Homo contained humans, Lemur contained four lemurs and a colugo, and Simia contained all the rest — it was, in modern terms, a wastebasket taxon for the primates. Linnaeus did not think that Homo should form a distinct group from Simia, classifying them separately mainly to avoid conflict with religious authorities. If we take this into account, Simia (including Homo) would be roughly equivalent to the Suborder Haplorrhini of the Primates (while Lemur would be roughly equivalent to the Suborder Strepsirrhini).