The life cycle of plants alternates between a diploid sporophytic and a haploid gametophytic generation. In contrast to human and animal which set aside a specialized cell lineage (germline) for reproduction in early embryogenesis, the germline of plant is formed de novo. Female gametophyte, or embryo sac, is a multicellular structure hosted in the ovule. Polygonum-type embryo sac is the most prevalent female gametophyte that occurs in about 70% of angiosperms. Plant sexual reproduction initiates from differentiation of somatic cell to archesporal cell. In majority of angiosperms, only a single archesporial cell is produced from hypodermal cell of the ovule primordium to a megaspore mother cell which produces four megaspores after meiosis. One megaspore becomes functional megaspore that forms a large eight-nucleate coenocytic cell after three rounds of nuclear mitosis. Subsequently, nuclear migration and fusion, and cellularization occur, leading to the formation of a mature female gametophyte with three antipodals, one central cell, one egg cell, and two synergids. Female gametophyte development undergoes a complicated and elaborately tuned process including cell fate specification, cell division, and differentiation. There are great interests to investigate ovule and female gametophyte development not only for crop improvement, but also for answers to fundamental biological questions. Breakthroughs have been made in understanding molecular mechanisms underlying germline specification, functional megaspore selection, nuclear division, migration and fusion, and cell fate determination of the gametophyte. Plant reproductive development is a concerted work of complex regulatory mechanisms. This chapter provides a detailed overview of advances in genetic regulation and molecular pathways leading to female gametophyte development. The origin and evolution of the Polygonum-type female gametogenesis are discussed briefly.