Book excerpt: We humans can enhance some of our mental and physical abilities above the normal upper limits for our species with the use of particular drug therapies and medical procedures. We will be able to enhance many more of our abilities in more ways in the near future. Some commentators have welcomed the prospect of wide use of human enhancement technologies, while others have viewed it with alarm, and have made clear that they find human enhancement morally objectionable. The Ethics of Human Enhancement examines whether the reactions can be supported by articulated philosophical reasoning, or perhaps explained in terms of psychological influences on moral reasoning. An international team of ethicists refresh the debate with new ideas and arguments, making connections with scientific research and with related issues in moral philosophy.