An instruction on certain bioethical questions, given on the Feast of the Nativity of the Blessed Virgin Mary, which updates Donum Vitae after twenty years of new biomedical developments. Its first part restates the anthropological, theological and ethical principles: the dignity of every human being from conception, and the dignity of marriage and procreation. The second examines new techniques of assisting fertility, freezing of embryos and oocytes, embryo reduction, preimplantation diagnosis and gene therapy. The third treats proposals that make use of human embryos or of material of illicit origin, including stem-cell research, cloning, hybrids and vaccines, and the question of cooperation in evil.