A procedure to cryopreserve mammalian embryos resulting in the birth of offspring was first described almost forty years ago. This procedure resulting in the birth of a child was reported 26 years ago. Since then, the preservation of human oocytes and embryos by cooling them to low subzero temperatures has become an integral part of Assisted Reproductive Technologies (ART). Hundreds of thousands of children have now been born after having been cryopreserved as oocytes or embryos. These results owe as much to the fundamental understanding of cryobiology as to the application of reproductive medicine. This brief review summarizes the history of embryo cryobiology, and presents a synopsis of basic cryobiology as it applies to present methods to improve the cryopreservation of human oocytes.