Recent studies have shown that components of the cell-cycle machinery can have diverse and unexpected roles in the retina. Cyclin-kinase inhibitors, for example, have been implicated as regulators of cell-fate decisions during histogenesis and reactive gliosis in the adult tissue after injury. Also, various mechanisms have been identified that can compensate for extra rounds of cell division when the normal timing of the cell-cycle exit is perturbed. Surprisingly, distinct components of the cell-cycle machinery seem to be used during different stages of development, and different organisms might rely on distinct pathways. Such detailed studies on the regulation of proliferation in complex multicellular tissues during development have not only advanced our knowledge of the ways in which proliferation is controlled, but might also help us to understand the degenerative disorders that are associated with gliosis and some types of tumorigenesis.