As our preface suggests, the ordinary use of the phrase “human enhancement” covers a wide range of practices, most of which are not explored in the enhancement ethics literature. To orient our tour, both “human” and “enhancement” merit some initial clarification, even before we pursue the ways they are interpreted and debated in the literature. For example, as section 2.3 below shows, equivocations between biological and evaluative senses of the term “human” are rich sources of many superficial disagreements in these debates. Is there anything special about being a member of the biological species homo sapiens that enhancements could threaten, or are those who criticize enhancement as “dehumanizing” really thinking about the loss of other markers of the moral status we confer on persons? To look ahead, we think it will become clear in the sections below that the ethical issues at the heart of the debate about human enhancement are not about policing the biological boundaries of the species homo sapiens. At this point, however, it is enough to note that we are foreclosing neither sense of “human” from the start, but will stay alert to both until it becomes important to distinguish and relate them.