With progress in genetic research advancing as it is, a host of novel theoretical and practical challenges are thereby being raised. From a bioethical perspective, it is easy to get the feeling that, because of this rapid progress, many fundamental concepts that should be in place arent yet in place. This lack may be felt especially in relation to human gene modification. with the Human Genome Projects potential to yield innumerable applications, one of the things that should be in place (...) is a set of fundamental conceptual guidelines demarcating the kinds of genetic modifications that should count as ethically acceptable and legally permissible. In this paper, my goal is to articulate such guidelines, specifically for the set of all possible human germline modifications. (shrink)