This chapter presents a classic, principlist approach to biomedical ethics, and its grounds in common morality and some of the moral theories. It reflects on the scope and limits of respect for autonomy, nonmaleficence, and beneficence in clinical practice and health policy. The chapter also identifies instances of justified and unjustified medical paternalism. It considers casuistry's critique of principlism and its positive approach to moral decisionmaking in bioethics. When faced with moral quandaries, principlism and casuistry are two alternative methods that can help professionals determine the right response. The Principle of Respect for Patient Autonomy captures a now commonly acknowledged duty in bioethics created by the right of patients and research subjects to make autonomous decisions. The Principle of Nonmaleficence captures parallel prohibitions in the context of clinical practice and research. The bioethics approach so far considered is principlist: it invokes general norms that express obligations in clinical practice and biomedical research.