What is animal intelligence? In what ways is it similar to human intelligence? Many behavioural scientists have realized that animals can be rational, can think in abstract symbols, can understand and react to human speech, and can learn through observation as well as conditioning many of the more complicated skills of life. Duane Rumbaugh and David Washburn have identified an advanced level of animal behaviour that reflects animals' natural and active inclination to make sense of the world. Rumbaugh and Washburn unify all behaviour into a framework they call Rational Behaviourism and present it as a new way to understand learning, intelligence and rational behaviour in both animals and humans. Drawing on years of research on issues of complex learning and intelligence in primates (notably rhesus monkeys, chimpanzees and bonobos), Rumbaugh and Washburn provide delightful examples of animal ingenuity and persistence, showing that animals are capable of very creative solutions to novel challenges. The authors analyse learning processes and research methods, discuss the meaningful differences across the primate order and point the way to further advances, enlivening theoretical material about primates with stories about their behaviour and achievements.