During the past two decades there has been an extraordinary proliferation of articles, books, reports, laws and regulations, and meetings concerned with the ethical aspects of biomedical interventions on human beings and, in particular, those of an experimental nature. Such writings, the vast majority of which are in the English language, necessarily tend to become more and more repetitive in the sense that they bring to light no new facts, or even ideas, but are variations on the same themes according to the cultural and professional backgrounds of their authors. For some of the older problems of medical ethics, particularly those linked to human reproduction— such as induced abortion, sterilization, and artificial insemination from a donor—it would be illusory to expect a consensus at the national, far less the international, level, for religious dogma or deeply-felt personal convictions may render discussion sterile. However, for the increasingly important subject of biomedical experimentation involving human subjects it might well be possible to arrive at an international consensus, as has already been done in very broad terms by the World Medical Association in the Tokyo (1975) revision of the Declaration of Helsinki (Helsinki II). It was in the belief that a more comprehensive consensus might be achieved that the World Health Organization and the Council for International Organizations of Medical Sciences embarked in 1978 on a joint project for the establishment of international ethical guidelines for biomedical research involving human subjects, taking Helsinki II as their starting point. In some of the existing literature on bioethics there are brief historical introductions, but these are usually very rudimentary. It was therefore decided that, in order to place the WHO/CIOMS project in the broadest possible perspective, an attempt should be made to provide a further, if not comprehensive, account of the historical aspects of human experimentation and of the circumtances in which formal ethical codes evolved.