The goal of this chapter is to present a view of the ways in which experience interacts with intrinsic forces in development o yield a functionally competent brain. The broad issue addressed is the manner in which the developing brain acquires its ability to guide the organism through the demands of a complex, changing environment and the manner in which the knowledge acquired through the evolutionary history of the species is combined with the knowledge acquired by the individual. We have attempted to write this chapter at a level that does not require extensive knowledge of the detailed workings of the nervous system to follow the basic logic. A warning is noted at the outset of some of the more daunting sections.