Categories straddle the boundary between the mind and the world: they are socially developed mental representations, but they must fit the properties of real objects in the real environment if they are to be useful. Concepts and Conceptual Development reflects the view that a full understanding of categorization must take all these constraints into account. Everyday terms and categories depend not only on the implicit theories that people have about the world (their 'idealised cognitive models'), but also on the objective properties of particular objects and the perceptible similarities among these objects. An understanding of these multiple relationships can reshape studies of concepts and conceptual development. Concepts and Conceptual Development draws together theorists from a wide range of theoretical orientations to consider many different aspects of 'the psychology of concepts'.