Human embryo cryopreservation is widely applied by programs of assisted reproductive technology. However, recent surveys have shown that relatively few in vitro fertilization programs in the United States substantially increase their per retrieval delivery rates through cryopreservation. While embryos may be successfully frozen and thawed at a range of developmental stages using several different cryoprotectants, the majority of in vitro fertilization programs use 1,2 propanediol to freeze early (pronuclear four-cell) embryos. Ultrarapid freezing techniques are under continued study; they have not yet been shown to offer any clinical advantage over slow freezing protocols. Although interest in oocyte cryopreservation remains high, experimental evidence shows that cryoinjury to human oocytes results in chromosome sorting defects, reduced fertilization, and compromised embryonic development. Micromanipulation of mammalian oocytes appears to have no deleterious effect on subsequent cryopreservation.