Is it permissible to use a human embryo in stem cell research, or in general as a means for the benefit of others? Acknowledging each embryo as an object of moral concern, Louis M. Guenin argues that it is morally permissible to decline intrauterine transfer of an embryo formed outside the body, and that from this permission and the duty of beneficence, there follows a consensus justification for using donated embryos in service of humanitarian ends. He then proceeds to show how this justification commands assent even within moral and religious views commonly thought to oppose embryo use. Beneath his moral reasoning lies a carefully constructed metaphysical foundation incorporating accounts of the ontology of development, embryos, and species. He also incisively discusses nonreprocloning, reprocloning, ectogenesis, and related scientific frontiers. This compelling philosophical study will interest all concerned to understand virtue and obligation in the relief of suffering.