The nature, possibility, and implications of ethics expertise (or moral expertise) in general and of bioethics expertise in particular has been the focus of extensive debate for over thirty years. What is ethics expertise and what does it enable experts to do? Knowing what ethics expertise is can help answer another important question: What, if anything, makes a claim of expertise legitimate? In other words, how does someone earn the appellation "ethics expert?" There remains deep disagreement on whether ethics expertise is possible, and if so, what constitutes such expertise and what it entails and legitimates. Discussion of bioethics expertise has become particularly important given the growing presence of bioethicists in the clinical setting as well as efforts to professionalize bioethics through codes of ethics and certification (or quasi-certification) efforts. Unlike in the law or in engineering, where there may be a body of knowledge that professional organizations or others have articulated as important for education and training of experts, ethics expertise admits of no such body of knowledge or required experience. Nor is there an entity seen as having the authority to articulate the necessary scope of knowledge. Questions about whether there is such a body of knowledge for particular areas within bioethics have emerged and played a central role in professionalization efforts in recent years, especially in the area of clinical ethics.