The idea of using a sperm cell to introduce exogenous DNA into an oocyte at the time of fertilization is of interest for simple production of transgenic mice. Since 1989, contradictory reports have appeared in the literature, but now this technology, so-called sperm-mediated gene transfer (SMGT), is considered reproducible. Concomitantly, in vivo transfection of sperm cells has also proceeded, including direct gene delivery into a testis, so-called testis-mediated gene transfer (TMGT), and gene transfer into seminiferous tubules. This review summarizes what has been achieved in the field of gene transfer via sperm cells.