In Uganda's Kibale National Park, the trees are dripping with monkeys. The park has one of the highest concentrations of primates on the planet. And primatologist Colin Chapman has spent a decade here getting to know them. From the leaf-eating red colobus monkey, to the once desperately endangered black-and-white colubus, to chimpanzees, our closest relations in the animal world--all contribute to the health of the forest, and all have come under Chapman's careful scrutiny. Chapman's simple questions (how many primates live here? in what size groups?) have led to some complex answers. What they reveal about monkey and chimp behaviour can help us save the forests where they live--and better understand our own societies.