Many tissues and organs are maintained by stem cell populations. Anatomical constraints, cell proliferation dynamics and cell fate specification all affect stem cell behaviour, but their relative effects are difficult to examine in vivo. E. Jane Albert Hubbard, Hillel Kugler and colleagues now use available data to build a computational model of germline development in C. elegans (see p. 47). In this model, germline cells move, divide, respond to signals, progress through mitosis and meiosis, and differentiate according to various local rules. Simulations driven by the model recapitulate C. elegans germline development and the effects of various genetic manipulations. Moreover, the model can be used to make new predictions about stem cell population dynamics. For example, it predicts that early cell cycle defects may later influence maintenance of the progenitor cell population, an unexpected prediction that the researchers validate in vivo. This general modelling approach could, therefore, prove to be a powerful tool for increasing our understanding of stem cell population dynamics.