Nick Gordon / Golden-white tassel-ear marmoset / Silky marmosets (Mico chrysoleucos / Callithrix chrysoleuca) aggression, Amazonia, Brazil

Suzi Eszterhas / Northern muriqui monkey (Brachyteles hypoxanthus) juvenile aged one year, in tree playing with its mother's tail, RPPN Feliciano Miguel Abdala, Atlantic Forest, Brazil. June.

Nick Hawkins / Central American spider monkey (Ateles geoffroyi) juvenile, Corcovado National Park, Costa Rica. January.

Nick Hawkins / White-faced capuchin monkey (Cebus capucinus) in Tenorio Volcano National Park, Costa Rica

Bernard Castelein / Guianan brown capuchin (Sapajus apella) chewing on branch, Pampas del Yacuma Protected Area, Bolivia

Bernard Castelein / Bolivian red howler (Alouatta sara), Pampas del Yacuma Protected Area, Bolivia

Claudio Contreras / Mantled howler monkey (Alouatta pigra), Yaxchilan Natural Monument, Lacandon Rainforest, southern Mexico, July

Claudio Contreras / Central American spider monkey (Ateles geoffroyi) juveniles hanging by tails and playing, Calakmul Biosphere Reserve, Yucatan Peninsula, Mexico, August

Suzi Eszterhas / Cotton-top tamarin (Saguinus oedipus), three climbing tree. Northern Colombia.

Suzi Eszterhas / Cotton-top tamarin (Saguinus oedipus), adult with two week old baby on back. Northern Colombia.

Suzi Eszterhas / Colombian red howler monkey (Alouatta seniculus) mother and baby in tree. Northern Colombia.

Alex Hyde / Brown / Tufted Capuchin (Cebus apella) family group in cloud forest, Manu Biosphere Reserve, Peru.

Ernie Janes / Black howler (Alouatta caraya) captive, occurs in South America.

Edwin Giesbers / Brown headed spider monkey (Ateles fusciceps) mother and baby, captive occurs in Central and South America.

Edwin Giesbers / Brown headed spider monkey (Ateles fusciceps) group resting together, captive occurs in Central and South America.

Edwin Giesbers / Golden lion tamarin (Leontopithecus rosalia) captive, occurs in the Atlantic Rainforest of Brazil. Critically endangered.

Mark Bowler / Black spider monkey (Ateles chamek) calling, captive, Peru.

Mark Bowler / Black capuchin, (Sapajus nigritus) female standing on hind legs, Rio de Janeiro, Brazil.

Cyril Ruoso / Man with Chamec spider monkeys (Ateles chamek) holding onto him as he walks through sanctuary. Ikamaperou Sanctuary, Amazon, Peru. October 2006.

Cyril Ruoso / Common woolly monkeys (Lagothrix lagotricha) climbing over keeper in Ikamaperou Sanctuary, Amazon, Peru. October 2006.

Cyril Ruoso / Keeper feeding Common woolly monkeys (Lagothrix lagotricha) in Ikamaperou Sanctuary, Amazon, Peru. October 2006.

Cyril Ruoso / Common woolly monkey (Lagothrix lagotricha) reaching forward, Ikamaperou Sanctuary, Amazon, Peru.

Dave Watts / Golden lion tamarin (Leontopithecus rosalia rosalia) captive in zoo. Occurs in Brazil.

Kevin Schafer / Guatemalan Black Howler Monkey (Alouatta pigra) Community Baboon Sanctuary, Belize, Central America. Endangered species.

Kevin Schafer / Guatemalan Black Howler Monkey (Alouatta pigra) Community Baboon Sanctuary, Belize, Central America. Endangered species.

Kevin Schafer / Guatemalan Black Howler Monkey (Alouatta pigra) calling, Community Baboon Sanctuary, Belize, Central America. Endangered species.

Kevin Schafer / Guatemalan Black Howler Monkey (Alouatta pigra) climbing, Community Baboon Sanctuary, Belize, Central America. Endangered species.

Kevin Schafer / Guatemalan Black Howler Monkey (Alouatta pigra) peering from behind vegetation, Community Baboon Sanctuary, Belize, Central America. Endangered species.

Ben Cranke / Black-striped capuchin (Sapajus libidinosus) using rock as a tool to break open palm nut, Parnaiba Headwaters National Park, Piaui, Brazil. August.

Ben Cranke / Black-striped capuchin (Sapajus libidinosus) using rock as a tool to break open palm nut Parnaiba Headwaters National Park, Piaui, Brazil. July.

Ben Cranke / Black-striped capuchin (Sapajus libidinosus) using rock as a tool to break open palm nut, Parnaiba Headwaters National Park, Piaui, Brazil. July.

Juan Carlos Munoz / Golden-headed lion tamarin (Leontopithecus chrysomelas) captive portrait, Apenheul Park, Netherlands.

Juan Carlos Munoz / Black howler monkeys (Alouatta caraya) male and two females calling from tree, captive, Apenheul Park, Netherlands.

Nick Gordon / Golden-white tassel-ear marmoset / Silky marmoset, male carrying twin babies (Mico chrysoleucos / Callithrix chrysoleuca) Amazonia, Brazil

Pete Oxford / Common squirrel monkey {Saimiri sciureus} Amazonia, Brazil

Stephen Dalton / Owl monkey (Aotus sp.) portrait, Panama.

Bruce Thomson / Silvery marmoset (Callithrix argentata ssp. melanura) relaxing on a branch, Pocone, Brazil.

Bruce Thomson / Brown capuchin (Cebus apella) looking down from branch, Pocone, Brazil.

Doug Wechsler / Male Mantled howler monkey (Alouatta palliata) on foot bridge, La Selva Biological Station, Costa Rica.

Paul Williams / Black howler monkey (Alouatta caraya) looking out from tree foliage, Belize, Central America.

Paul Williams / Black howler monkey (Alouatta caraya) nibbling on leaves, Belize, Central America.

Paul Williams / Black howler monkey (Alouatta caraya) amongst tree foliage, Belize, Central America.