Despite our impression of a seamless spatial world, mature human spatial knowledge is composed of sub-systems, each specialized. This book uses the case of Williams syndrome - a rare genetic deficit - to argue for specialization of function in both normal and unusual development. The evidence suggests a speculative hypothesis linking the genetic deficit to changes in the timing of emergence for different sub-systems. More broadly, the book shows the complexity ofspatial cognition, its genetic correlates, and realization in the brain.