Extended culture to blastocyst is a common first-line approach to embryo selection in many IVF laboratories. Blastocyst transfer is associated with higher implantation and live birth rates than cleavage-stage embryo transfer in good prognosis patients. A blastocyst is the consequence of self-selection, having overcome morphogenetic hurdles, including activation of its own embryonic genome during early embryonic development. Improved uterine and embryonic synchronicity prevents premature exposure to the uterine environment. Blastocyst culture offers time for the gonadotrophin-induced raise in oestrogen levels to subside and enhances embryo–endometrium synchronisation with reduced uterine contractility. Evidence of epigenetic changes in blastocyst culture is weak, and babies born after blastocyst transfer have a similar chance of being healthy as those born after cleavage-stage embryo transfer. In-vivo pre-implantation embryo loss from cleavage-stage to blastocyst remains quantitatively undefined. Blastocyst culture should be routine in all IVF cycles as a strategy for selecting the most viable embryos for their implantation potential.