Our ability to alter the course of human development ranks among the most significant changes in modern science. We can choose the sex of our children in advance, and could potentially prevent disease with genetic enhancement. An ethical question then arises as to whether or not these things should be done. The goal of this book is to present enough science so that readers can both make an informed analysis of these issues. The chapters are not meant to provide definitive answers but, rather, to be springboards for discussion. The presentation of topics follows the same sequence used in most developmental biology courses. While the science has been simplified and explained at the level of an introductory biology course, it successfully conveys the essential information for useful discussions.