Renowned philosophers and medical ethicists debate and discuss the profoundly important concepts of disease and health. Christopher Boorse begins with an extensive reexamination of his seminal definition of disease as a value-free scientific concept. In responding to all those who criticized this view, which came to be called "naturalism" or "neutralism," Boorse clarifies and updates his landmark ideas on this crucial question. Other distinguished thinkers analyze, develop, and oftentimes defend competing, nonnaturalistic theories of disease. Their combined thoughts review and update an issue of central importance in bioethics today.