This chapter discusses the advantages of blastocyst transfer and reviews the clinical data. Improvements in the environment and the quality in the embryology laboratory, in culture media, and in the equipment used to produce embryos and embryo selection methods have all had positive impacts on the results of embryo transfers. Parental factors also affect blastocyst development and subsequent implantation rates. In order to optimize embryo culture and blastocyst transfer, one needs to consider all aspects of a treatment cycle. Vitrification is now already the preferred method of cryopreserving embryos of the mouse and cow, and it is only a matter of time before this elegant procedure supercedes slow freezing in the clinical laboratory. Once the blastocyst is biopsied, and therefore collapsed, it is vitrified. Subsequently, a single euploid blastocyst with the highest developmental potential, as determined through morphological grading and noninvasive assays of physiology, is transferred to a natural uterus.