This Element examines three related topics in the field of bioethics that arise frequently both in clinical care and in medico-legal settings: capacity, informed consent, and third-party decision-making. All three of these subjects have been shaped significantly by the shift from the paternalistic models of care that dominated medicine in the United States, Canada, and Great Britain prior to the 1960s to the present models that privilege patient autonomy. Each section traces the history of one of these topics and then explores the major ethics issues that arise as these issues are addressed in contemporary clinical practice, paying particular attention to the role that structural factors such as bias and social capital play in their use. In addition, the volume also discusses recent innovations and proposals for reform that may shape these subjects in the future in response both to technological advances and changes in societal priorities.