The basic principles of the development of the central nervous system (CNS) are reviewed,and their implications for both normal and abnormal development of the brain are discussed. Thegoals of this review are (a) to provide a set of concepts to aid in understanding the variety ofcomplex processes that occur during CNS development, (b) to illustrate how these conceptscontribute to our knowledge of the normal anatomy of the adult brain, and (c) to provide a basisfor understanding how modifications of normal developmental processes by traumatic injury, byenvironmental or experiential influences, or by genetic variations may lead to modifications inthe resultant structure and function of the adult CNS.