Germ cell development is a step-wise process that ensures the progression of the life cycle due to their unique ability to transmit their genome from one generation to the next. In the mouse, the precursors of germ cells, the Primordial Germ Cells (PGCs), arise at the onset of gastrulation. Here we discuss how PGCs acquire their fate in the epiblast and outline their development until their arrival into the gonads. Male germ cell tumors (GCTs) have a similar gene expression pattern to that of fetal germ cells and to pluripotent cells, suggesting that GCT originate from an alteration of gonocyte normal development. We evaluate coincidences and differences in germ cell development in mouse and humans and on this basis, we speculate future research perspectives.