This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book addresses a number of general questions concerning consent. It explores the moral relevance of consent and its relations to other issues in normative ethics. The book discusses the importance of consent for various topics in legal theory. It is concerned with the importance of consent in several areas of medical ethics. The book traces the role of consent in the history of medical ethics, looks at ancient Greece, medieval Europe, the Middle East, and the development in Western law and ethics. It deals with the scope and the force of the modern informed consent requirement. The book suggests that similar to the way in which consent can be nullified if it fails to meet certain standards of validity, the lack of actual consent to political authority can be nullified if the people in question are morally required to consent.