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Polarization is a mechanism commonly used by cells to establish asymmetries and create specialized subcellular functional domains. The process of cell polarization is especially important during mammalian development, when pluripotent cells are first established. Pluripotent cells are, by definition, capable of giving rise to the entire fetus. In addition, pluripotent stem cell lines can be derived from mammalian embryos and can be created by reprogramming differentiated cells. Understanding the molecular and cell biological differences between pluripotent and nonpluripotent cells is an important research direction in regenerative medicine. This chapter focuses on examining the role that cell polarization plays in establishing and maintaining pluripotency in the mouse embryo and in pluripotent stem cell lines. The literature shows that, in the early embryo, cell polarization is repressed in emerging pluripotent epiblast cells, while apicobasal polarization is established in multipotent cells of the extraembryonic lineages. Since polarization of extraembryonic cells is essential for defining which cells become pluripotent, cell polarization is indirectly responsible for establishing pluripotency in the embryo. Later, in the established pluripotent epiblast, cells polarize just before they exit pluripotency and commence differentiation. Just as multiple stages of pluripotency exist in the embryo, multiple pluripotent states exist among stem cell lines, ranging from naive to primed pluripotency. Mirroring the embryonic stages of pluripotency, polarity is associated with primed, and not naive, pluripotent stem cell lines. Therefore, in both embryos and in stem cell lines, cell polarization is a hallmark of decreased developmental potential, suggesting that the purpose of pluripotent cell polarization is to prepare cells for the next developmental goal: differentiation.