The focus here is the question of the moral status of viable human embryos for the first few days of their existence. More precisely, my focus is the human embryo from its conception, through its becoming a mass of undifferentiated cells, to its first differentiation when the initial stem cell mass appears. Naturally, this would occur in the first week of the embryo’s existence, whether in vitro (in a laboratory) or in vivo (in the uterine tubes or uterus). With cryogenics, the process can be frozen at any stage. In this essay, I identify four categories of human embryos and argue that differences between these categories support the view that embryos are not all equal in terms of their moral status, which, in turn, supports the legitimacy of some medical and research procedures that put embryos at risk.