Organogenesis relies on the orchestration of many cellular interactions to create the collective cell behaviours needed to shape developing tissues. Yoshiki Sasai and colleagues have developed a three-dimensional cell-culture system in which floating clusters of mouse embryonic stem cells can successfully organize themselves into a layered structure resembling the optic cup, a pouch-like structure that develops into the inner and outer layers of the retina during embryogenesis. In further 3D culture, the optic cup forms fully stratified retinal tissue as seen in the postnatal eye. This approach might have important implications for stem-cell therapy for retinal repair. The optic cup shown on the cover was generated from multi-photon images of an optic cup formed in vitro.