A primate ( /ˈpraɪmeɪt/ US dict: prī′·māt) is a mammal of the order Primates (/praɪˈmeɪtiːz/ US dict: prī·mā′·tēz; Latin: "prime, first rank"), which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment. All but a few primate species remain at least partly arboreal.

With the exception of humans, who inhabit every continent, most primates live in tropical or subtropical regions of the Americas, Africa and Asia. Primates range in size from Madame Berthe's mouse lemur, which weighs only 30 grams (1 oz), to the Eastern lowland gorilla, weighing over 200 kilograms (440 lb). According to fossil evidence, the primitive ancestors of primates may have existed in the late Cretaceous period around 65 million years ago; the oldest known primate is the Late Paleocene Plesiadapis, c. 55–58 million years ago.Molecular clock studies suggest that the primate branch may be even older, originating in the mid-Cretaceous period around 85 mya.