Including my time as a trainee in the labs of two leaders in the field, I have worked for 25 years on mammalian spermatogenesis. Thus, I have a broad range of experiences studying all phases of male germ cell development, from fetal prospermatogonia to ejaculated sperm. My NIH-funded laboratory uses transgenic and knockout mouse models along with pharmacologic interventions and in vitro spermatogenesis as models to define essential regulatory molecules, pathways, and processes that drive meiotic initiation as well as the production and function of sperm.