In this long-awaited work, Philip Hershkovitz provides the most thorough and comprehensive treatise ever published on New World monkeys. The volume gives a detailed account of the origin, evolution, dispersal, and behavior of platyrrhines and a systematic arrangement of all known forms, living and extinct. During an eleven-year period, Hershkovitz examined more than 3,100 museum-preserved specimens and relevant primate fossils and observed hundreds of animals in captivity and thousands in the wild state. He presents his results in an elegant and encyclopedic text, lavishly illustrated with 520 figures and 7 color plates. Hershkovitz opens the study with a brief history and a definition, characterization, and comparison of primates as a taxonomic unit. Basing his work on nearly all known genera of living primates, the author deals with New World monkeys from comparative anatomical and evolutionary points of view. He examines display characters, pelage, the evolution of color patterns, primate locomotion, cranial and dental morphology, and the central nervous system. The final and most extensive part of the volume is devoted to the taxonomy and biology of the family Callitrichidae, comprising marmosets and tamarins, and the family Callimiconidae, represented by the callimico alone. Hershkovitz concludes with an exhaustive bibliography of more than 2,500 published works and a gazetteer of essential geographic data.