Purinergic signalling plays a major role in the function of every organ including the brain. A growing body of evidence also suggests that purinergic signalling is important in the development of the retina, cochlea and neocortex. In these three contexts release of ATP through the spontaneous gating of connexin hemichannels, in cells respectively of the retinal pigment epithelium, Köllicker’s organ, and the radial glia, triggers waves of intracellular Ca²⁺ release. In the case of the developing retina and cortex, the released ATP acts to control proliferation of neuronal precursor cells, while in the cochlea it coordinates the spontaneous activity of adjacent hair cells to refine the tonotopic maps in the cochlear nucleus. Recently ATP-derived ADP signalling has been implicated at the very earliest stages of development, notably in triggering the gene expression necessary for formation of the eye. It is now timely to test the extent to which connexin hemichannel mediated ATP release and accompanying Ca²⁺ waves contribute to all stages of development.