What is informed consent? The answer may seem self-evident only to those who have yet to explore the many meanings of the term. Informed consent refers to legal rules that prescribe behaviors for physicians and other healthcare professionals in their interactions with patients and provide for penalties, under given circumstances, if physicians deviate from those expectations; to an ethical doctrine, rooted in our society’s cherished value of autonomy, that promotes patients’ right of self-determination regarding medical treatment; and to an interpersonal process whereby these parties interact with each other to select an appropriate course of medical care. Informed consent is each of these things, yet none of them alone. As a theory based on ethical principles, given effect by legal rulings and implemented by clinicians, it has been haunted by its complex lineage. When legal principles and ethical values conflict, which should take precedence? When clinical interests appear to be served by neither legal nor ethical concerns, which interests should be compromised and to what degree? The vast literature on informed consent, found in journals and books of medicine, law, bioethics, philosophy, and public policy, has been stimulated by the need to create a workable doctrine that can accommodate values that to many observers are in an irremediable state of conflict. The conflicts in theory and the need to resolve them in practice are the subjects of this book. Theory is the focus of the first half of the volume; practice is the topic of the second. Seeking to understand the fascinating theoretical problems requires us to grapple with some of the most difficult ethical and policy issues facing our society today. But let us state at the outset our belief that the clinician on the front lines need not be paralyzed by differences of opinion among legal and ethical theorists. Through the vaguely translucent wall of expertise behind which the discussion about the proper shape of the informed consent doctrine has taken place, a reasonable approach to informed consent in the clinician-patient relationship can be discerned. Our most important and challenging task in this book is to make that approach evident.