Over the past decade, we have begun to understand the molecular genetics of cranial nerve development through the analysis of mouse mutants. Nerve identity is imparted by genes involved in anteroposterior patterning, such as the Hox genes, kreisler and Krox20. Neuronal determinants, including Lim homeobox genes, dictate neuronal subtype along the dorsoventral axis. Subsequent neuronal differentiation, and cell body and axon migration, is governed by subtype-specific gene expression, which is transient at times. So far, only a few cranial-axon-specific guidance molecules have been identified. The insights from these genetic analyses will help to guide future analyses of cranial nerve development in vertebrates.