In this paper, I discuss the significance of informed consent( IC) at the time of its origin in the United States. There are two settings wherein IC is applied ― human research and clinical medicine. In clinical medicine, two legal principles ― battery and negligence ― are relevant in lawsuits. I show that the core of IC comprises the principle of “negligence,” whose significance is clarified in this paper in detail. This principle means “an enlargement of the scope of doctors’ responsibility”, which urges us to redefine the relationship between doctors and patients. Finally, on these grounds, I consider the ethical implications of “self-determination of patients.” The essence of IC is that it changes the order of priority, from the previous relation, “the benefit of the patient > the will of the patient,” to the current relation “the will of the patient > the benefit of the patient”. In other words, the essence of IC is to respect the will of patients and provide medical benefits by assisting them.