The cumulus mass is a group of cells surrounding the oocyte. Cumulus cells are known to play a role in a number of reproductive events including oocyte maturation and acrosome reaction. Calcium mobilization in cumulus cells has been implicated in the process of oocyte maturation and acrosome reaction; however, its exact role remains elusive. In this review, we summarize the findings on Ca(2+) mobilization in cumulus cells, with particular focus on (1) the gonadotropin/paracrine factors-induced cumulus Ca(2+) mobilization and its downstream signaling pathways in oocyte maturation and (2) the sperm-derived factors-induced cumulus Ca(2+) mobilization in the cross-talk between cumulus and sperm and thus acrosome reaction. The evidence suggests that as an important signaling event, Ca(2+) mobilization in cumulus cells is important to germ cell development and function, and thus essential to fertilization and reproduction.