Monkeys are broadly divided into Old World species (160 species) and New World species (174 species) for a total of 334 species altogether!

A number of countries have used monkeys in their space programs, including the United States and France. Albert II, a rhesus monkey, was the first mammal in space. He flew to an altitude of 83 miles (134 km) aboard a U.S. V-2 rocket on June 14, 1949. Unfortunately, Albert died upon reentry after a parachute failure caused his capsule to impact the ground. A previous monkey, Albert I, died when the V-2 rocket failed before reaching peak altitude.

Some organizations train capuchin monkeys as service animals to assist quadriplegics and other people with severe spinal cord injuries or mobility impairments. After being socialized in a human home as infants, the monkeys undergo extensive training before being placed with disabled people. Around the house, the monkeys assist with daily tasks such as feeding, fetching, manipulating objects, and personal care.

A group of monkeys, regardless of species, is called a troop or barrel. The term "barrel" was first recorded in the 1800s and inspired the classic children's toy Barrel of Monkeys produced by the Milton Bradley Company, which included a series of interlocking monkeys stored in a toy barrel.

The pygmy marmoset is a small genus of New World monkey native to rainforests of the western Amazon Basin in South America. Notable for being the world's smallest monkey, it weighs just 3.5 oz at adulthood (about as much as a deck of cards) and is generally found in evergreen and river-edge forests, where it is a gum-feeding specialist, or a gummivore.

The low and guttural sound of howler monkeys is one of the loudest calls produced by any land animal. Under certain conditions, a howler's call can be heard from up to 3 miles (4.8 kilometers) away!

Emperor tamarin monkeys are often called moustache monkeys because their most distinctive feature is a long, drooping moustache of white hairs that stands out against their gray to black coats.

Panamanian white-faced capuchins (Cebus capucinus) have odd greeting rituals such as poking each other in the nose to say hello and build social connections.

Hanuman, a human-like monkey god who is believed to bestow courage, is a prominent deity in Hinduism. The meaning of the word "Hanuman" is unclear, but one interpretation is "one having a disfigured jaw." This version is supported by a Puranic legend wherein the infant Hanuman mistakes the Sun for a fruit, attempts to pluck and eat it, and is wounded in the jaw for his troubles.

In the 1940s, researchers studying the Japanese macaque at Koshima Island left sweet potatoes on the beach for them to eat. One female, named Imo (Japanese for yam or potato) didn't like the taste of the dirt on the veggies, so she washed them off in the river. After a while, others started to copy her behavior. Today, washing food has become a learned behavior, passed down from generation to generation, making the Japanese macaque unique since no other monkeys in the world are known to wash their food before eating.