During the development of the mammalian CNS, multipotent progenitors generate the three major neural cell lineages (neurons, oligodendrocytes and astrocytes) at specific times and places. But what coordinates the generation of these cell types? On p. 1617, Sugimori and co-workers suggest that the combined action of two classes of transcription factors holds the answer. The researchers use in vitro (rat neurosphere assay) and in vivo (genetic and gene expression studies in mice) approaches to examine neurogenesis and oligogenesis in the developing ventral spinal cord. They report that Pax6, Olig2 and Nkx2.2 - transcription factors that specify the positional identity of the multipotent progenitors -are also involved in the timing of neural cell differentiation. These`patterning factors' do this, the researchers show, by modulating the activities of proneural (Ngn1, Ngn2, Ngn3 and Mash1) and inhibitory (Id1 and Hes1) helix-loop-helix transcription factors. Thus, they propose, these two classes of transcription factors form a molecular code that controls the spatiotemporal pattern of neuro/gliogenesis.