New World monkeys of the Saimiri are known as squirrel monkeys. The Saimiri is the only one in the Saimirinae family. The Tupi origin of the name is sai-mirm or ai-mbirn, which means'monkey' and'small', and was also used as an English name by early researchers. Squirrel monkeys live in the tropical forests of Central and South America in the canopy layer. Most species have parapatric or allopatric ranges in the Amazon.

There are two main groups of squirrel monkeys recognized. They are differentiated based on the shape of the white coloration above the eyes. In total there are 5 recognized species.

Squirrel monkeys are able to sweat through their hands and feet. Their hands and feet can be made to feel damp by this. Squirrel monkeys need to use other thermoregulation techniques such as behavioral changes and urine washing if they want to maintain proper osmoregulation in high temperatures and high humidity. Color vision studies have been performed on squirrel monkeys for the purpose of understanding vision ailments in humans.

Squirrel monkeys have short and close fur colored black at the shoulders, yellow or orange fur along the back and extremities, and white on the face.