The female gametophyte represents an essential portion of the plant life cycle mediating several reproductive processes, including pollen tube guidance, fertilization, the induction of seed development, and maternal control of seed development. During the past few years, genetic approaches in Arabidopsis and maize have provided us with molecular and genetic information about megagametogenesis and the induction of seed development. However, we still know little about pollen tube guidance, fertilization, and the maternal control of seed development at the molecular level. In addition, a comprehensive profile of the genes expressed in the female gametophyte has not been obtained. In light of the fact that a large proportion of female gametophytic genes are expected to have partially or completely redundant functions (Drews and Yadegari, 2002), a combination of forward- and reverse-genetics approaches will be required to completely understand the development and reproductive functions of the female gametophyte.