During neurogenesis, Notch ligands expressed by differentiating neurons inhibit the differentiation of neighbouring cells. This `lateral inhibition'maintains a pool of progenitor cells next to differentiating neurons within which neurogenesis can be initiated when the neuron migrates away from the neural epithelium. Now, David Wilkinson and colleagues report that Lunatic fringe (Lfng), a Notch modifier best known for its roles in boundary formation, promotes the lateral inhibition of neurogenesis in the zebrafish hindbrain (see p. 2523). The researchers show that Lfng is expressed by neural progenitors in neurogenic regions of the hindbrain and is downregulated in cells that have initiated differentiation. Loss-of-function studies and analysis of mosaic embryos reveal that Lfng is required cell autonomously to limit the amount of neurogenesis in the hindbrain and to maintain neural progenitors. Based on their results, the researchers suggest that Lfng acts in a feedback loop that, by promoting Notch activation, maintains the competence of progenitor cells to receive lateral inhibition from differentiating neurons.