The pygmy marmoset or dwarf monkey is a New World monkey native to the rainforest canopies of western Brazil, southeastern Colombia, eastern Ecuador, eastern Peru, and northern Bolivia. It is one of the smallest primates, and the smallest true monkey, with its body length ranging from 14 to 16 centimetres (5.5 to 6.3 in) (excluding the 15-to-20-centimetre (5.9 to 7.9 in) tail). Males weigh around 140 grams (4.9 oz), and females only 120 grams (4.2 oz).

Despite its name, the pygmy marmoset is somewhat different from the typical marmosets, most of which are classified in the genera Callithrix and Mico; as such, it is accorded its own genus, Cebuella.

Nicknames for this monkey often refer to its diminutiveness, for example: mono de bolsillo ("pocket monkey"), leoncito ("little lion"), and finger monkey.

The pygmy marmoset uses special types of communication to give alerts and warning to its family members. These include chemical, vocal, and physical types of communication. A trill is used to communicate over long distance. A sharp warning whistle and a clicking sound signal danger to their family members. A J-call is a series of fast notes repeated by the caller and is used at medium distances.^{[citation needed]}