New World monkeys are the five families of primates that are found in Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Platyrrhini parvorder and the Ceboidea superfamily, which are essentially synonymous since Ceboidea is the only living platyrrhine superfamily. They differ from other groupings of monkeys and primates, such as the Old World monkeys and the apes.

New World monkeys are small to mid-sized primates, ranging from the Pygmy Marmoset (the world's smallest monkey), at 14 to 16 cm (5.5 to 6.3 in) and a weight of 120 to 190 grams (4.2 to 6.7 oz) to the Southern Muriqui, at 55 to 70 cm (22 to 28 in) and a weight of 12 to 15 kg (26 to 33 lb). New World monkeys differ slightly from Old World monkeys in several aspects. The most prominent phenotype distinction is the nose, which is the feature used most commonly to distinguish between the two groups. The scientific name for the New World monkeys, Platyrrhini, means "flat nosed". The noses of New World monkeys are flatter than the narrow noses of the Old World monkeys, and have side-facing nostrils. New World monkeys are the only monkeys with prehensile tails—in comparison with the shorter, non-grasping tails of the anthropoids of the Old World.

The New World is one of the names used for the Western Hemisphere, specifically the Americas and sometimes Oceania (Australasia). The term originated in the early 16th century, shortly after America was discovered by European explorers, expanding the geographical horizon of the people of the European Middle Ages, who had thought of the world as consisting of Europe, Asia, and Africa only: collectively now referred to as the Old World. The Americas were also referred to as the "fourth part of the world".

The term was first coined by the Florentine explorer Amerigo Vespucci, in a letter written to his patron Lorenzo di Pier Francesco de' Medici in the Spring of 1503, and published (in Latin) in 1503-04 under the title Mundus Novus. Vespucci's letter contains arguably the first explicit articulation in print of the hypothesis that the lands discovered by European navigators to the west were not the edges of Asia, but rather an entirely different continent, a "New World".