The cryopreservation of human oocytes and blastocysts is an important topic in assisted reproduction. The placement of human oocytes, zygotes, and embryos inside a hermetically closed container before plunging into liquid nitrogen for vitrification permits a reliable isolation of the cells from the liquid nitrogen and avoids the potential for contamination by microorganisms. Efficient aseptic vitrification of oocytes and embryos can be performed with decreased concentrations of permeable cryoprotectants and complete isolation of embryos from liquid nitrogen. This chapter presents a vitrification procedure for different stages of oocytes during maturation, including fertilized embryos and blastocysts. Using dimethyl sulfoxide (DMSO) for vitrification of oocytes was also successful, with a high survival rate of warmed oocytes, on going clinical pregnancy, and later birth of healthy babies after embryo transfers. Osmosis plays a central role in all the negative effects of the cryopreservation process for human pronuclear embryos.