This review discusses the role that the sperm-specific phospholipase C zeta (HA) is proposed to play during the fertilization of mammalian eggs. At fertilization, the sperm initiates development by causing a series of oscillations in cytosolic concentrations of calcium [Ca-2] within the egg. PLC zeta mimics the sperm at fertilization, causing the same pattern of Ca2+ release as seen at fertilization. Introducing PLC zeta into mouse eggs also mimics a number of other features of the way in which the fertilizing sperm triggers Ca2+ oscillations. We discuss the localization of PLC zeta within the egg and present a hypothesis about the localization of PLC zeta within the sperm before the initiation of fertilization. (C) 2014 Elsevier Inc. All rights reserved.