Supernumerary embryos may be cryopreserved as early as day 1 (pronuclear stage) and up to day 6 or day 7. This chapter focuses on the crypreservation of pronuclear stage embryos on day 1. Two main methods are used for the cryopreservation of human oocytes and embryos: slow freezing and vitrification. Although controlled slow freezing remains the main method of cryopreservation in most in vitro fertilization (IVF) programs, the vitrification technique has entered the mainstream of human assisted reproductive technology (ART) more and more. Successful pregnancies and live births have been achieved by vitrification of human oocytes and embryos using different carrier systems. The total concentration of cryoprotectant ranges from 5 to 8 mol/l in vitrification protocols currently used in the cryopreservation of human oocyte and embryos. Relatively limited data are available regarding the application of vitrification in the cryopreservation of pronuclear stage human embryos.