The molecular mechanisms that control regional specification, morphogenesis and differentiation of the embryonic forebrain are not known, although recently several laboratories have isolated homeobox, Wnt and other genes that are candidates for playing roles in these processes. Most of these genes exhibit temporally and spatially restricted patterns of expression within the forebrain. However, analysis of the spatial patterns has been complicated because an understanding of the organization of the embryonic forebrain has been lacking. This article describes a neuromeric model of the forebrain that is consistent with the expression patterns of these genes, and that provides a framework for understanding the morphological relationships within this complex structure.