Colobine monkeys have a unique digestive system, analogous to that of ruminants, which allows them to exploit foliage as a food source. This gives them a niche in Old World forests where they are often the only abundant medium-sized arboreal folivorous mammal. From a possible Miocene origin, Colobine monkeys have radiated into a wide variety of forms inhabiting a range of tropical woodlands in Africa and Asia. Most of the extant species have been subject to long term field studies, but until this book, no synthesis of work on this group has been available. The central theme is that of adaptive radiation, showing how the special features of Colobine anatomy interacted with a range of ecosystems to produce the distinctive species of today. The book also discusses parallels with other mammalian groups.