Making a functional nervous system involves the production of specific types of neurons in characteristic locations and their ability to find and synapse with appropriate target cells. By capitalizing on the advanced genetics and molecular biology of Drosophila, a rapidly growing number of genes have been identified that control these events. Studies of the expression and function of these genes in single, uniquely identified cells is possible because of the relative simplicity of the Drosophila embryonic nervous system. A class of neurogenic genes, including N, Dl, and E(spl), controls the emergence of the entire neuronal precursor population, whereas some of the segmentation genes, such as ftz and eve, control the fates of individual neurons. Later in development, genes encoding cell-surface molecules, called fasciclins, may be involved in the ability of growing neurons to recognize and elongate axons along specific pathways to reach their synaptic targets.