Human adults appear different from other animals in their ability to form abstract mental representations that go beyond perceptual similarity. In short, they can conceptualize the world. This apparent uniqueness leads to an immediate puzzle: WHEN and HOW does this abstract system come into being? To answer this question we need to explore the origins of adult concepts, both developmentally and phylogenetically; When does the developing child acquire the ability to use abstract concepts? Does the transition occur around 2 years, with the onset of symbolic representation and language? Or, is it independent of the emergence of language? When in evolutionary history did an abstract representational system emerge? Is there something unique about the human brain? How would a computational system operating on the basis of perceptual associations develop into a system operating on the basis of abstract relations? Is this ability present in other species, but masked by their inability to verbalise abstractions? Perhaps the very notion of concepts is empty and should be done away with altogether. This book tackles the age-old puzzle of what might be unique about human concepts. Intuitively, we have a sense that our thoughts are somehow different from those of animals and young children such as infants. Yet, if true, this raises the question of where and how this uniqueness arises. What are the factors that have played out during the life course of the individual and over the evolution of humans that have contributed to the emergence of this apparently unique ability? This volume brings together a collection of world specialists who have grappled with these questions from different perspectives to try to resolve the issue. It includes contributions from leading psychologists, neuroscientists, child and infant specialists, and animal cognition specialists. Taken together, this story leads to the idea that there is no unique ingredient in the emergence of human concepts, but rather a powerful and potentially unique mix of biological abilities and personal and social history that has led to where the human mind now stands. A 'must-read' for students and researchers in the cognitive sciences.