 In its most important role in bioethics, informed consent is a legitimacy requirement for certain actions. Inadequately informed consent makes certain intrusions impermissible. Roughly, when a sufficiently capacitated adult does not give sufficiently informed and voluntary consent to intervention in her body or her private sphere, then, at least when the intervention is substantial, not trivial, and absent severe jeopardy for third parties, the intervention is impermissible—even when it seeks to assist her, physicians recommend it, third parties would benefit from it, and the patient herself had repeatedly consented to it before expressing a change of mind. When the antecedent is inapplicable—for instance, when the patient lacks decision-making capacity—similarly spirited rules apply, such as rules delegating consent “authority” to the patient’s  advance directive  or proxy.