It is argued that action constitutes the foundation for cognitive development. Action is a principal component of all aspects of cognitive development including social understanding. It reflects the motives of the child, the problems to be solved, the goals to be attained, and the constraints and possibilities of the child's body and sensory-motor system. Actions are directed into the future and their control is based on knowledge of what is going to happen next. The child's sensory-motor system is especially designed to facilitate the extraction of this knowledge. In addition, the infant is endowed with motives that ensure that these innate predispositions are transformed into a system of knowledge for guiding actions. By acting on the world, infants develop their cognition.