The discovery and development of information surrounding the retinoic acid receptors (RAR and RXR) has ushered in a new era in understanding the molecular mechanism of action of vitamin A in embryonic development and cellular differentiation. The mechanisms involved in the regulation of gene expression by the retinoids is at least partially known and involves binding of the RAR and RXR to retinoic acid response elements. Additional factors, including coregulatory proteins, associated regulatory elements, and cell-specific factors, may also be involved in determining the specificity of retinoid-regulation of gene expression during development. During embryogenesis, retinoids are required for the development of the posterior hindbrain and its associated structures, as well as for the survival and differentiation of certain classes of neurons and neural crest cell derivatives. At least some of the effects of retinoid on hindbrain development are related to the regulation of Hox gene expression. Additional retinoid-regulated genes have been implicated in nervous system development, and the manner in which they lead to phenotypic changes during embryogenesis remains to be determined.