Sperm and eggs are essential cells for reproduction and fertility in mammals. Lack of sperm production is one of the leading causes of infertility, a major and growing problem in the developed world affecting 13 to 18% of reproductive-age couples. The birth of the first test tube baby by in vitro fertilization marked an advance in infertility treatment. Later on, several important new techniques called assisted reproductive technologies were developed to help couples who experience infertility. One limiting factor is the requirement of reproductive cells (gametes) for use in in vitro fertilization. For azoospermic men lacking sperm cells, producing gametes in vitro could be a new window to overcome infertility. In the past few years, several reports have been published on generating germ cells from stem cells, one of the epitomes of which was the report on functional in vitro-derived (IVD) germ cells. These mature haploid sperm cells from mouse embryonic stem cells were capable of egg fertilization and producing live offspring. In tandem with previous advancements in germ cell research, development of new technologies based on IVD gametes will change the future of infertility and provide a new basis for the establishment of novel therapeutic approaches to cure more complicated conditions of infertility. In addition, IVD gametogenesis provides an accessible system for studying the specification and differentiation of sperm cells and related processes such as meiosis, morphogenesis, and motility.