There are a lot of cute monkeys to choose from, but squirrel monkeys might be the most memorable of them all. Hailing from Central and South America, these primates offer more than just looks: They're also smart. In fact, they're known to have the largest brain-to-body-mass ratio of all the monkey species. That intelligence explains their endless curiosity, and helps them keep track of their intricate social relationships. Troops of squirrel monkeys are known to reach as many as 500 members.
Unfortunately, their charismatic nature also makes them a popular species in the illegal pet trade.