<p>Human germ cells are the foundation of human reproduction and development, ensuring heredity and contributing to genetic diversity. Accordingly, their anomalies lead to critical diseases, including infertility. Recent advances in genomics and stem cell-based in vitro gametogenesis research have expanded our knowledge of how human germ cells are specified and differentiate during embryonic and fetal development, elucidating evolutionarily distinctive as well as conserved properties of human germ cell development. Here, based on the evidence from both in vivo and in vitro studies, we provide an integrated review of the progress in our understanding of human embryonic and fetal germ cell development, encompassing germ cell specification, epigenetic reprogramming and sex-specific germ cell development. Knowledge of the mechanisms of human germ cell development will enable its in vitro reconstitution, which in turn will serve as a foundation for innovative medical strategies to prevent germ cell-related diseases, including infertility.</p>