In 1972, cryopreservation of mammalian animal embryos was developed using mouse embryos. To utilize surplus embryos for in vitro fertilization programs, this technique was applied to human embryos by the slow freezing method in the first half of the 1980's, and by vitrification in the 1990's. Recently, the protocol of vitrification of human embryos has been improved by the ultra-rapid vitrification method in which the rate of cooling is highly improved. It is mainly used as an effective basic technique for cryopreservation of human embryos in current clinical IVF programs due to the extremely high embryonic survival rate after storage.