Plant reproduction occurs through the production of gametes by a haploid generation, the gametophyte. Flowering plants have highly reduced male and female gametophytes, called pollen grains and embryo sacs, respectively, consisting of only a few cells. Gametophytes are critical for sexual reproduction, but detailed understanding of their development remains poor as compared to the diploid sporophyte. This article reviews recent progress in understanding the mechanisms underlying gametophytic development and function in flowering plants. The focus is on genes and molecules involved in the processes of initiation, growth, cell specification, and fertilization of the male and female gametophytes derived primarily from studies in model systems.