One important principle during neurogenesis in vertebrates as well as invertebrates, is the fact that neural progenitors generate different cell types in a reproducible temporal order. In Drosophila this change of temporal identity of neuroblasts (NBs) is linked to a sequential expression of the transcription factors Hunchback (HB), Krüppel (KR), PDM, Castor (CAS) and Grainyhead (GRH). We and others have shown that HB and KR are indeed decisive for the fate of the early born cells in certain NB lineages. In principal, these genes are consecutively expressed in a given NB in a certain time window, with expression continuing in the ganglion mother cell (GMC). At the end of each time window the expression is switched off in the NB but stays on in the GMC and its progeny. Thus, the temporal specification of NB progeny depends strongly on the correct timing of the on and off switch of these genes within the NB and the GMCs. Our recent results show that the dynamic expression of hb is mainly brought about by an antagonistic regulation of seven up (svp) and prospero (pros). Taken together these data provide first principal insights into how developmental time is transformed into the generation of specific cell fates by stem cells.