During the early stages of embryonic development, a small population of cells is set aside to form the germline. These primordial germ cells (PGCs) are often specified separate in time and space from their eventual home, the developing gonads. PGCs must therefore undertake a journey through the developing tissues of the embryo to reach their destination and ensure the fertility of the organism. Despite decades of interest in this topic and significant progress made in other model organisms, there is still very little known about how this migration is accomplished in the mouse or any other mammal. In this review, I explore over half a century of work examining this enigmatic cell and its voyage through the mouse embryo, interpreting these findings in light of recent discoveries in the field of cell migration. I discuss possible migration modes used by mouse PGCs, changes in their microenvironment that could influence migration, and roles the nucleus might play in their journey. With modern advances in microscopy and transgenic reporter mice, it is time to delve into this fascinating and important model of cell migration in vivo.