Informed consent is a process through which patients or their surrogates authorize medical interventions or involvement in research. The concept of informed consent is supported by ethical principles and legal tradition in the United States. It grew in importance during the 20th century because of documented abuse of research subjects, which led to its codification in federal consent requirements for clinical research. For the most part, the concept and the codification are based on a model of competent patients who are capable of informed decision-making and can communicate their wishes. However, most critically ill patients are incompetent and cannot communicate easily. As a result, family members usually must give consent for them. Yet family members frequently are unavailable, and when they are available, they may not know the patient's wishes. Furthermore, family members may not be legally authorized to give consent for research involvement under state law. For these and other reasons, it has been argued that the concept of informed consent is not applicable to clinical research involving the critically ill and that such consent is not necessary in certain circumstances. Yet, for all its inadequacies, the concept of informed consent and the federal consent requirements should be retained because they promote respect for patients and their right of self-determination and because investigator discretion is not adequate. Stronger research oversight may be as important as informed consent in protecting patient welfare.