A significant number of current developments in the field of Biotechnology –such as stem cells, in vitro fertilization, embryo research, cloning, among others– are related directly or indirectly to the beginning of human life. It is important to acknowledge the biological status of the human embryo: when does its life begin and what is it from a biological standpoint. Therefore, by considering such information, informed choices could be made in moral and legal issues. The different biological processes of fertilization are presented, noting particularly when human life begins. Based on these biological facts some basic principles are proposed to establish a moral and legal regulation.