Mammalian germ cells do not determine their sexual fate based on their XX or XY chromosomal constitution. Instead, sexual fate is dependent on the gonadal environment in which they develop. In an ovary, germ cells enter meiosis during fetal life, thereby committing to oogenesis. In a testis, germ cells commit to the spermatogenic programme of development during fetal life, although they do not enter meiosis until puberty. We aim to understand how somatic cells of the ovary and testis direct germ cells towards the appropriate sexual fate and how the innate pluripotency of germ cells is controlled to ensure fertility but avoid tumorigenesis. Understanding these networks is important in the contexts of etiology, diagnosis and treatment of infertility and gonadal cancers, and efforts to augment human and animal fertility using stem cell approaches. The particular focus for this presentation is on the mitosis-to-meiosis switch that occurs in germ cells of the fetal ovary.