Spermatogonial stem cells (SSCs) are responsible for the preservation of spermatogenesis throughout a man’s adult reproductive life. Like other stem cells in the body, SSCs can either self-renew or differentiate. The proliferation is a well regulated mechanism and is mainly directed by the Sertoli cells by the production of growth factors. The existence of SSCs offers clinically relevant options for preservation and re-establishment of the progenetive potential in the male. Especially the spermatogonial stem cell transplantation technique (SSCT) could prove important for fertility restoration in young cancer patients. This technique relies on the injection of SSCs from a fertile donor in an infertile recipient testis. Other approaches to preserve male fertility have also been described. Testicular tissue grafting can be applied to generate spermatozoa from spermatogonial stem cells in a host and cryopreservation of SSCs will be of great importance when these techniques become available for clinical use. However SSCT is considered the most promising tool for fertility preservation, this technique is not without risk. It is obvious that reintroduction of malignant  cells into a cured patient must be omitted. Decontamination of suspensions by FACS or MACS can solve this problem. SSCs might as well be selected out of a testicular cell suspension by using SSC markers. A number of markers has recently been identified. Next to fertility preservation, SSC studies can be useful for other applications as well, such as transgenerational gene therapy, male infertility, male contraception and the treatment of germinal tumors.