The principle of beneficence directs healthcare practitioners to promote patients’ well-being, ensuring that the patients’ best interests guide treatment decisions. Because there are a number of distinct theories of well-being that could lead to different conclusions about the patient’s good, a careful consideration of which account is best suited for use in the medical context is needed. While there has been some discussion of the differences between subjective and objective theories of well-being within the bioethics literature, less attention has been (...) given to the questions of what work a theory of well-being needs to do in bioethics and which standards of success ought to be used in selecting a theory of well-being for use in medicine. In this article, I argue that traditional theories of well-being developed in philosophy are not well suited to meet the needs of the medical context. For the principle of beneficence to be most useful, the underlying account of well-being should satisfy two conditions: first, it needs to lead to a concrete, action-guiding determination of the patient’s good; and, second, any recommendations it offers need to be justifiable to patients. Standard accounts of well-being have difficulty satisfying both conditions. Exploring the limitations of these theories when applied to treatment dilemmas helps point the way toward the development of an account of well-being better suited to healthcare. (shrink)